Baffle plate, apparatus for producing the same, method of producing the same, and gas processing apparatus containing baffle plate

ABSTRACT

The present invention provides a gas process apparatus that realizes uniform exhaust without depending on process conditions, a gas process chamber that constitutes the gas process apparatus, a baffle plate mounted on the gas process chamber, a method of producing the baffle plate, and an apparatus for producing the baffle plate. The baffle plate of the present invention serves as a partition between a process space in which a chemical process is carried out with a supplied gas, and a duct that is adjacent to the process space and functions to discharge exhaust gas generated as a result of the chemical process. In accordance with the difference between the pressures on both sides of the baffle plate, which difference varies depending on the location on the baffle plate, the baffle holes are disposed on a plurality of locations on the baffle plate.

TECHNICAL FIELD

[0001] The present invention relates to a gas processing apparatus thatdischarges exhaust gas generated as a result of chemical processing, toa baffle plate incorporated into the gas processing apparatus, and amethod of and apparatus for producing the baffle plate.

BACKGROUND ART

[0002]FIG. 1 shows the structure of an apparatus that performs singlewafer processing in a hermetically sealed chamber used in a waferpreprocessing step of semiconductor production. As shown in FIG. 1, theprocessing apparatus comprises: a wafer placing stand 3 on which a wafer1, a glass substrate, and other electronic material substrates areplaced; an exhaust duct 5 that surrounds the wafer stand 3; a baffleplate that is provided with baffle holes 7 and placed on the exhaustduct 5; and an exhaust pipe 11 that is connected to the exhaust duct 5.In FIG. 1, arrows 13 indicate the exhaust flow of the process gas.

[0003] To perform uniform processing on the surface of the wafer 1 inthe apparatus for performing single wafer processing in a hermeticallysealed chamber, for instance, in a CVD (Chemical Vapor Deposition)apparatus, an etching apparatus, an annealing apparatus, and a drycleaning apparatus, it is necessary to supply the process gas uniformlyon the surface of the wafer 1 with a shower head, and to flow theexhaust gas generated from the contact with the wafer 1 in the radialdirection evenly at any circumferential angle of the wafer 1 (thisprocess will be hereinafter referred to as “uniform exhaust”).

[0004] The uniform exhaust is essential in the single wafer processingapparatus (such as a metallic CVD apparatus) to perform a uniform filmforming operation. The single wafer processing apparatus that performs aso-called rate-determining process in which the reaction rate on thesurface of the wafer 1 depends on the transportation rate of thematerial gas. Also, in a plasma processing apparatus in which theresidence time of the gas on the wafer has an influence on theconcentration variation of labile species (i.e., in a plasma CVDapparatus or a plasma etching apparatus), the uniform exhaust isessential for obtaining a uniform film forming rate and an etching rate.

[0005] In a normal case where the connecting port of the exhaust pipe 11connected to the pump for exhausting the wafer processing gas deviatesfrom the center axis of the wafer 1 and opens toward the gas processingchamber, it is difficult to exhaust the gas evenly from the center ofthe gas flow on the wafer in the every circumferential direction. Inorder to solve this problem, the exhaust duct 5 is extended from theconnecting port of the exhaust pipe 11 to the entire periphery of thewafer 1, and the baffle plate 9 is disposed as a separation wall onboundary between the exhaust duct 5 and the chamber. Normally, a numberof baffle holes 7 are formed at uniform intervals in the baffle plate 9,thereby obtaining uniform exhaust.

[0006] The baffle plate 9 aims to decrease unevenness of exhaust gasflow on the surface of the wafer 1. The principles of the baffle plate 9reside in forming the baffle holes 7 that causes a greater flowresistance than the flow resistance in the exhaust duct 5 so as toreduce a variation in exhaust conductance that depends on thecircumferential angle and to make the flow rate of the exhaust gasaround the wafer 1 uniform in the circumferential direction.

[0007] To make the exhaust flow rate of the baffle holes 7 uniform, itis necessary to equalize the differential pressures at the respectivebaffle holes 7 on both sides of the baffle plate 9. However, in aconventional technique of forming the identical baffle holes 7 on thebaffle plate 9 at uniform intervals, it is difficult to obtain uniformexhaust flow 13 at every circumferential angle of the wafer 1. The mainreason for this is that the difference between the inner pressure of theexhaust duct 5 and the pressure in the chamber in the normal filmforming operation is small. As a result, the adverse influence of theinner pressure of the exhaust duct 5 on the variation of thedifferential pressures due to a fluid pressure loss becomes too great toignore.

[0008] It may be possible to reduce the pore size of each baffle hole 7so as to increase the differential pressures on both sides of bafflehole 7 to such a degree that can nullify a variation of the innerpressure of the exhaust duct 5. However, a smaller pore size of eachbaffle hole 7 will results in an increase of the pressure in thechamber. Enlarging the pore size of each baffle hole 7 to reduce theflow resistance in the exhaust duct 5 is also undesirable, because alarger pore size results in a decrease of the flow resistance in theexhaust duct 5. Accordingly with the conventional apparatus employingthe baffle plate 9, there remain problems that a relatively large amountof exhaust gas flows on the surface of the wafer in the vicinity of theconnecting port of the exhaust pipe 11, and that the flow rate of theexhaust gas at the connecting port of the exhaust pipe 11 and at thebaffle holes 7 on the other side is low.

[0009] In order to solve the above problems, Japanese Laid-Open PatentApplication No. 63-141318 discloses a conductance plate provided with aplurality of holes having pore sizes proportional to the distances fromthe exhaust port. However, such a conductance plate does not functionsufficiently to obtain uniform processing on a number of samples.

[0010] Furthermore, a conventional exhaust device has a simple structurehaving the exhaust pipe 11 connected to the side wall of the gasprocessing chamber (such a structure will be hereinafter referred to as“sidedraft exhaust structure”). In this conventional exhaust device, anexhaust port is normally formed on the side wall, causing muchunevenness in exhaust gas flow. In order to solve such a problem, astructure having two or more connecting ports on the side wall of thegas processing chamber has been suggested, as disclosed in JapaneseLaid-Open Patent Application No. 8-45917. With such a structure,however, the unevenness of exhaust gas flow can be corrected to somedegree, but there is another problem that the structure becomescomplicated, resulting in higher production costs.

[0011] As disclosed in Japanese Laid-Open Patent Application No.63-111621, an exhaust device that exhausts from below the wafer stand inthe coaxial direction with the central axis of the wafer has beensuggested. With such an exhaust device, there are problems that theconfiguration of the exhaust device becomes too long in the central axisdirection, and that the arrangement of various components (such as thewiring arrangement for a pusher pin for moving up and down the wafer, asuscepter heater, and a temperature heater) that are normally arrangedbelow the wafer stand becomes difficult.

[0012] Also, in the conventional exhaust device using a porous baffleplate in a gas process chamber having a sidedraft exhaust structure, ithas been difficult to designing and produce a uniform-exhaust baffleplate that can obtain uniform distribution of the flow rate of anexhaust gas in the circumferential direction on the wafer. The biggestreason of this is that a quantitative design method which is based onhydrodynamic theories was unknown. More specifically, as the baffle poresize becomes smaller, the exhaust flow rate becomes more uniform.However, the chamber inner pressure increases at the same time. As aresult, this technique is not applicable to a normal process in whichthe chamber inner pressure needs to be low.

[0013] Meanwhile, Japanese Laid-Open Patent Application No. 8-64489discloses a structure in which the baffle holes are arranged at variedintervals, and Japanese Patent No. 2927211 discloses a baffle plateprovided with exhaust conductance adjusting holes that are displaced.However, it has been considered difficult to obtain an exhaust devicethat has a function to maintain uniform exhaust regardless of variousprocess conditions such as the gas flow rate, the type of gas,temperatures and pressures. Even if the diameters and intervals of thebaffle holes are varied, it is difficult to maintain predetermineduniformity in exhaust, except under specially prescribed processconditions.

[0014] Japanese Laid-Open Patent Application No. 62-98727 reads that “Asshown in FIG. 2, a plurality of exhaust holes 10 are designed inaccordance with the fluid conductance calculated from the flowingdirection of an etching gas flowing from a gas introduction path 4uniformly downward along the surface of the wafer 6”. However, thisreference only suggests that the pore size should be larger as thelocation of the hole becomes more distant from the main exhaust hole,while mentioning no detailed method or technique for designing theexhaust holes.

DISCLOSURE OF THE INVENTION

[0015] An object of the present invention is to provide a gas processapparatus that realizes uniform exhaust regardless of processconditions, a baffle plate that is mounted on the gas process apparatus,a method of producing the baffle plate, and an apparatus for producingthe baffle plate.

[0016] The above objects of the present invention are achieved by abaffle plate that parts a process space in which a chemical process iscarried out with a supplied gas from a duct that is adjacent to theprocess space for discharging an exhaust gas generated as a result ofthe chemical process. In this baffle plate, after a plurality of throughholes are virtually formed at desired locations on the baffle plate, theplurality of through holes are actually formed at the desired locationso that flow rates of the exhaust gas at the plurality of through holesbecome uniform. With this baffle plate, uniform exhaust required for thechemical process can be surely realized.

[0017] The above objects of the present invention are also achieved by abaffle plate that parts a process space in which a chemical process iscarried out with a supplied gas from a duct that is adjacent to theprocess space for discharging an exhaust gas generated as a result ofthe chemical process. In this baffle plate, through holes are formed ata plurality of locations on the baffle plate, depending on pressuredifferences between two sides of the baffle plate. With this baffleplate, uniform exhaust required for the chemical process can be surelyachieved.

[0018] In the above baffle plate, the through holes may be formed inaccordance with a pressure variation of the exhaust gas along a flowingpath of the exhaust gas inside the duct. More specifically, throughholes may be formed so that the flow rates of the exhaust gas flowingthrough the through holes calculated in accordance with theHagen-Poiseuille's law become constant. The above objects are alsoachieved by a baffle plate having at least three through holes atvarious intervals, or a baffle plate having at least two through holeshaving different pore sizes.

[0019] The above objects of the present invention are also achieved by abaffle plate that parts a process space in which a chemical process iscarried out with a supplied gas from a duct that is adjacent to theprocess space for discharging an exhaust gas generated as a result ofthe chemical process, and a plurality of through holes are formed atdesired locations. This baffle plate varies in thickness at two or morelocations among the desired locations. With this baffle plate, theconductance of the exhaust gas flowing through the through holes can beadjusted.

[0020] The above objects of the present invention are also achieved by abaffle plate that parts a process space in which a chemical process iscarried out with a supplied gas from a duct for exhausting an exhaustgas generated as a result of the chemical process. In this baffle plate,slits that penetrate through the baffle plate and vary in width alongwith a flowing path of the exhaust gas in the duct are formed inaccordance with pressure differences between both sides of the baffleplate, the pressure differences varying depending on locations on thebaffle plate. With this baffle plate, the conductance of the exhaust gasflowing through the slits can be adjusted.

[0021] The above objects of the present invention are also achieved by abaffle plate that parts a process space in which a chemical process iscarried out with a supplied gas from a duct that is adjacent to theprocess space so as to discharge an exhaust gas generated as a result ofthe chemical process. In this baffle plate, slits that penetrate throughthe baffle plate and have uniform widths are formed along a flowing pathof the exhaust gas inside the duct, and the baffle plate varies inthickness along the flowing path.

[0022] The above objects of the present invention are also achieved by agas process apparatus that comprises: a process space including a standon which an object to be processed is placed, and a gas supply unit forsupplying a gas to the object to be processed so as to perform achemical process on the object placed on the stand; a duct that isadjacent to the process space so as to discharge an exhaust gasgenerated as a result of the chemical process; and a discharging unitthat is connected to the duct for discharging the exhaust gas. This gasprocess apparatus is characterized by further comprising a partitionunit that parts the duct from the process space, and adjusts the flowrate of the exhaust gas flowing from the process space to the ductdepending on pressure differences between both sides of a boundarysurface, the pressure differences varying with locations on the boundarysurface between the process space and the duct. With this gas processapparatus, uniform exhaust required for the chemical process can besurely realized.

[0023] The above objects of the present invention are also achieved by amethod of producing a baffle plate that parts a process space in which achemical process is carried out with a supplied gas from a duct that isadjacent to the process space so as to discharge an exhaust gasgenerated as a result of the chemical process. This method ischaracterized by comprising the steps of: calculating pressuredifferences between both sides of the baffle at desired locations on thebaffle plate; and forming through holes at a plurality of locations onthe baffle plate, depending on the calculated pressure differences. Bythis method, a baffle plate that can realize uniform exhaust can besurely obtained.

[0024] The above objects of the present invention are also achieved by amethod of producing a baffle plate that parts a process space in which achemical process is carried out with a supplied gas from a duct that isadjacent to the process space so as to discharge an exhaust gasgenerated as a result of the chemical process. This method ischaracterized by comprising the steps of: calculating pressuredifferences between both sides of the baffle plate, the pressuredifferences varying with locations on the baffle plate, and a pressurevariation of the exhaust gas along a flowing path of the exhaust gasinside the duct; and forming through holes at a plurality of locationson the baffle plate in accordance with the calculated pressuredifferences and the pressure variation.

[0025] The above objects of the present invention are also achieved by amethod of producing a baffle plate that parts a process space in which achemical process is carried out with a supplied gas from a duct that isadjacent to the process space for discharging an exhaust gas generatedas a result of the chemical process. This method is characterized bycomprising the step of forming a plurality of through holes in thebaffle plate so that a flow rate of the exhaust gas calculated inaccordance with the Hagen-Poiseuille's law becomes constant.

[0026] The above objects of the present invention are also achieved by amethod of producing an apparatus for producing a baffle plate that partsa process space in which a chemical process is carried out with asupplied gas from a duct that is adjacent to the process space fordischarging an exhaust gas generated as a result of the chemicalprocess. This apparatus is characterized by comprising: a calculatingunit that calculates pressure differences between both sides of thebaffle plate at various locations on the baffle plate; and a holeforming unit that forms through holes at a plurality of locations on thebaffle plate in accordance with the pressure differences calculated bythe calculating unit.

[0027] In the above apparatus, the calculating unit calculates apressure variation of the exhaust gas along a flowing path of theexhaust gas inside the duct, and the hole forming unit forms the throughholes at the plurality of locations on the baffle plate in accordancewith the pressure differences and the pressure variation calculated bythe calculating unit.

[0028] The above objects of the present invention are also achieved byan apparatus for producing a baffle plate that parts a process space inwhich a chemical process is carried out with a supplied gas from a ductthat is adjacent to the process space for discharging an exhaust gasgenerated as a result of the chemical process. This apparatus ischaracterized by comprising: a calculating unit that calculates holeforming locations so that flow rates of the exhaust gas at through holesformed in the baffle plate calculated in accordance with theHagen-Poiseuille's law become uniform; and a hole forming unit thatforms the through holes at the hole forming locations calculated by thecalculating unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 shows the structure of an apparatus for processing singlewafers in a hermetically sealed chamber in a wafer preprocessing insemiconductor production procedures;

[0030]FIG. 2 shows a gas flow and a differential pressure in an exhaustduct;

[0031]FIG. 3 shows the structure of a conventional baffle plate;

[0032]FIG. 4 shows the structure of a gas process chamber on which thebaffle plate of FIG. 3 is mounted;

[0033]FIG. 5 illustrates the arrangement of baffle holes formed in thebaffle plate of a first embodiment of the present invention;

[0034]FIG. 6 shows the structure of the baffle plate of the firstembodiment of the present invention;

[0035]FIG. 7 shows the structure of a baffle plate of a secondembodiment of the present invention;

[0036]FIG. 8 is a graph showing the characteristics of the baffle plateprovided with baffle holes having different pore sizes from each otherin accordance with the second embodiment of the present invention;

[0037]FIG. 9 is a graph showing the results of a simulation performed onthe conventional baffle plate shown in FIG. 3 under the same conditionsas in the case shown in FIG. 8;

[0038]FIG. 10 is a graph showing the results of a simulation performedon a conventional baffle plate disclosed in Japanese Laid-Open PatentApplication No. 63-141318;

[0039]FIG. 11 shows the structure of a baffle plate of a thirdembodiment of the present invention;

[0040]FIG. 12 shows the structure of a gas process chamber on which thebaffle plate shown in FIG. 11 is mounted;

[0041]FIG. 13 shows the structure of a baffle plate of a fourthembodiment of the present invention;

[0042]FIG. 14 shows the structure of a gas process chamber on which thebaffle plate shown in FIG. 13 is mounted;

[0043]FIG. 15 shows the structure of a baffle plate of a fifthembodiment of the present invention;

[0044]FIG. 16 shows the structure of a has process chamber on which thebaffle plate shown in FIG. 15 is mounted;

[0045]FIG. 17 shows the structure of a baffle plate of a sixthembodiment of the present invention;

[0046]FIG. 18 shows the structure of a gas process chamber on which thebaffle plate shown in FIG. 17 is mounted;

[0047]FIG. 19 shows the structure of a gas process chamber of an eighthembodiment of the present invention;

[0048]FIG. 20 is a plan view of the gas process chamber shown in FIG.19;

[0049]FIG. 21 shows the structure of an apparatus for producing a baffleplate of the present invention; and

[0050]FIG. 22 is a flow chart showing an operation of producing thebaffle plate shown in FIG. 21.

BEST MODE FOR CARRYING OUT THE INVENTION

[0051] The following is a description of embodiments of the presentinvention, with reference to the accompanying drawings. Throughout thedrawings, the same components are denoted by the same referencenumerals.

[0052] In the embodiments of the present invention, equations areemployed for virtually determining the shapes and sizes of bafflepassages, the diameters and intervals of baffle holes, the number ofbaffle holes, the widths of slits, and the thickness variation of thebaffle plate. Based on values calculated using those equations, baffleplates having the optimum shapes for obtaining circumferentially uniformflow rates of a gas flowing on the wafer will be specified in thefollowing description.

[0053] A baffle plate having the fluid-mechanically optimum shape islogically proved to be capable of obtaining uniform exhaust, regardlessof process conditions such as the flow rate of a process gas, the typeof the process gas, temperatures, and pressures.

[0054] The basic ideas of the embodiments of the present invention areto design the baffle passages for making the exhaust gas flow uniform insuch a manner that equalizes the exhaust conductance from a givenlocation near the wafer 1 to the connecting port of the exhaust pipe ofthe chamber. In order to achieve this, the pressure loss due to thefluid friction of the gas flowing toward the connecting port of theexhaust pipe needs to be evaluated for each gas passage. The mostnoteworthy pressure loss is caused between the fluid resistance of abaffle passage and the fluid resistance of a gas flowing through theexhaust duct on the downstream of the baffle passage. To obtain thosefluid pressure losses, the Fanning's equation or the Hagen-Poiseuille'slaw are used, so that the baffle passages are designed based on thelogical relationship between the shape and size, and the flow rates anddifferential pressures of the baffle holes or the baffle slits andexhaust duct.

[0055] The relational expressions between the differential pressures,the flow rates, and the pore sizes are basically essential logicalequations for designing the optimum shape of a baffle plate that canobtain uniform exhaust. For instance, the flow rate of a baffle hole ora slit is proportional to the fourth power of its pore size,proportional to the third power of the slit width, inverselyproportional to the plate thickness, and proportional to the square ofthe difference between the pressure above the passage and the pressurebelow the passage. The shape of the passage for uniform exhaust in thecircumferential direction is determined based on a variation of the ductinner pressure, which varies in a wide range due to an increase of thegas flow rate on the downstream side in the duct. However, a highlyanalytical technique has been required for determining the threefactors, i.e., the shapes, the flow rates, the pressures of thepassages.

[0056] Under the above conditions, five types of baffle plates havingthe optimum shapes were designed and produced based on the newlyintroduced logical equations. These baffle plates were then mounted on asingle wafer process apparatus to obtain uniform exhaust. The five typesinclude: 1) a uniform-size, uniform-thickness porous baffle plate thathas baffle holes arranged at varied intervals for obtaining uniformexhaust; 2) a uniform-interval, uniform-thickness porous baffle platethat has baffle holes having varied pore sizes for uniform exhaust; 3) auniform-size, uniform-interval porous baffle plate that varies inthickness for uniform exhaust; 4) a uniform-thickness slit-type baffleplate that has slits having varied widths for uniform exhaust; and 5) auniform-width slit baffle plate that varies in thickness for uniformexhaust.

[0057] Among the above baffle plates, the easiest one for processing isthe baffle plate 1) having baffle holes arranged at varied intervals.This structure can be easily obtained by forming holes having differentangles in the circumferential direction using cutting blades of the samediameter. In this manner, uniform exhaust can be achieved at a low cost.On the other hand, with the above baffle plate 2) having baffle holeshaving varied pore sizes, it is necessary to prepare many cutting bladeshaving different diameters. Meanwhile, the baffle plates 3) and 5) thatvary in thickness in the circumferential direction are relatively easyto produce. However, it is not so easy to produce the baffle plate 4)having slits that vary in width. Despite the varied difficulties inproduction, the optimized baffle plates have the same uniform exhaust,and can be effectively used in a single wafer process chamber.

[0058] In the above baffle plate 4), slits are formed for exhaust, andthe widths of the slits are continuously varied in thefluid-mechanically optimum manner, so that the smallest necessarypressure loss can be obtained for uniform exhaust. On the other hand, aporous baffle plate requires a relatively great differential pressure,and the pressure in the gas process chamber unnecessarily rises.

[0059] To avoid the above problems, the embodiments of the presentinvention provide porous baffle plates and slit-type baffle plates thatcan obtain uniform exhaust in a single wafer process chamber by a newdesign method. Also, the embodiments of the present invention provide agas process apparatus including any one of the above baffle plates. Sucha gas process apparatus may be applied to any one of apparatuses, suchas etching apparatuses, plasma apparatuses, and thermal CVD (ChemicalVapor Deposition) apparatuses.

[0060] In the following, the basic theoretical formulas of the presentinvention will be described. In a single wafer processing apparatushaving a sidedraft exhaust structure, a gas enters the exhaust duct 5from the surface of the wafer 1 through the baffle holes 7 around thewafer 1. After going half around inside the exhaust duct 5, the gasreaches the connecting port of the exhaust pipe 11 disposed on the sidewall of the gas processing chamber. Here, the flow rate at each bafflehole 7 is determined by the difference between the inner pressure of theexhaust duct 5 and the pressure in the chamber. This relationship can beexpressed by a Hagen-Poiseuille's law that holds between the flow rateand the pressure difference in a case where viscous flow passes throughthe fluid passage.

ΔP=32 μLu/D ²  (1)

[0061] wherein D indicates the inner diameter [m] of the fluid passage,L indicates the length [m] of the fluid passage having the innerdiameter D, ΔP indicates the differential pressure [Pa] with thepressure at the downstream of the distance L, μ indicates the viscosityof the gas [Pa·sec], and u indicates the flow rate of the gas [m/sec].

[0062] Taking the variation of the volume due to a pressure intoaccount, an equation using a mass velocity G [kg/m²/sec] can be obtainedas will be shown later.

[0063] The Hagen-Poiseuille's law is originally a relational expressionwith respect to a fluid pressure loss caused when a viscous fluidlaminar-flows through fluid passages in a circular duct. In a case wherethe fluid are not circular, a representative size called an equivalentdiameter is used, instead of the diameter of a circle, to obtain thesame relational expression. According to “Chemical Engineers' Handbook(5th revised edition)” (edited by Chemical Engineering Society, andissued by Maruzen), the equivalent diameter is a value obtained bymultiplying a hydraulic radius by 4. The hydraulic radius is obtained bydividing the cross section area of the passage by the circumferenceadjacent to the fluid on the cross section of the passage. In thefollowing, the cross section of the fluid passage is circular for easeof explanation, but the same effects can be achieved by using theequivalent diameter when the cross section of the fluid passage is notcircular.

[0064] As for the laminar flow region in a range to which theHagen-Poiseuille's law is applied, the Reynolds' number of the gas flowin the apparatus to which the present invention is applied is 100 orsmaller. When the Reynolds' number is 2000 or smaller, it is normallypossible to maintain laminar flow. As for the applied pressure range, 20pascal or greater should be enough to obtain viscous flow. Even at a lowpressure, 10 pascal should be enough in practical use, as long as thediameter of the fluid passage is 20 or more times as great as the meanfree path of gas molecules.

[0065] It should be noted that the mean free path of nitrogen moleculesat 20 Pa and 200° C. is approximately 500 μm, which is sufficientlysmall, compared with the equivalent diameter, 27 mm, of the duct in thefollowing embodiments. The diameters of the passages of the baffle holesare smaller than the diameter of the duct, but the pressure is higher inthe baffle passages. As a result, the mean free path should be muchsmaller. At 93.3 Pa, for instance, the mean free path should beapproximately 100 μm. Accordingly, the following equation should hold inpractical use.

ΔP= ⁰ P−{ ^(C) P ²−64 μLRTG/MD ²}^(0.6)  (2)

[0066] wherein the ⁰P indicates the pressure [Pa] at the referencepoint, R indicates the gas constant (8.3143 [m² kg/mol/sec²]), Tindicates the temperature [K], and M indicates the molecular weight[kg/mol].

[0067]FIG. 2 shows the gas flow and differential pressure in the exhaustduct. As shown in FIG. 2, numbers i=1, 2, 3, . . . are allocated to thebaffle holes from the most downstream side of the exhaust duct. Here,the relationships among the pore size D_(i), the pore length L_(i), theduct inner pressure P_(i), the gas flow rate F_(i), the differentialpressure Δ⁰P_(i) between the process chamber pressure ⁰P and the ductinner pressure P_(i), the differential pressure (pressure variation)ΔP_(i+1,i) between the duct inner pressure P_(i+1) below the holeadjacent to the fluid passage of the exhaust gas and the duct innerpressure P_(i), the equivalent diameter D_(H) of the duct, and thelength L_(i+1,i) of the passage of the duct from the ith hole and thei+1 the hole, are expressed by the following equations. Here, when thecross section of the passages of the duct is not circular, for instance,when the cross section is a rectangle having a long side a and a shortside b, the equivalent diameter of the duct should be 2ab/(a+b).

P _(i+1) =P _(i) +P _(i+1,i)  (3)

Δ⁰ P _(i)=⁰ P−P _(i)  (4)

F _(i)=(π/4)(0.0224D _(i) ² /M)G _(i)/(1E−6/60)[sccm]  (6)

P ₁={⁰ P ²−64L _(i) RTG _(i) /Md _(i) ²}^(0.6)  (5)

[0068] The equation (5) that expresses P_(i) can be transformed into anequation (7) by an equation (6) that expresses the hole gas flow rateF_(i) and the mass velocity G_(i).

P _(i)={⁰ P ²−64 μL _(i) RTF _(i)(1E−6/60)(1/0.0224)/(D _(i)⁴/4)}^(0.5)  (7)

[0069] With the substitution of δ (=64 μRT(1E-6/60)(1/0.0224)), theequation (7) can be further transformed into the following equation (8).

P _(i) ²=⁰ P ² −δL _(i) F _(i)/(πD _(i) ⁴/4)  (8)

[0070] From the above equation (8), the flow rate F_(i) of each hole canbe expressed by the following equation (9) as functions of the ductinner pressure P_(i), the inner diameter D_(i), and the hole lengthL_(i).

F _(i)=(⁰ P ² −P _(i) ²)(πD _(i) ⁴/4)/(δLi)  (9)

[0071] Meanwhile, the duct inner pressure P_(i) is expressed by theproduct of the downstream pressure and the differential pressure in thefollowing equation (10).

P _(i) =P ₁ +ΔP _(2,1) +ΔP _(3,2) +ΔP _(4,5) . . .+ΔP _(i,i−1)  (10)

[0072] The inner differential pressure of two neighboring holes in theduct is expressed by the following equation (11).

ΔP _(i,i−1) =P _(i) +ΔP _(i−1)  (11)

[0073] By substituting the equation (8) in the above equations (10) and(11), the following equation (12) can be obtained.

ΔP _(i,i−1) =P _(i) −{P _(i) ² −δL _(i,i−1) F _(i,i−1)/(πD _(H)⁴/4)}^(0.5)  (12)

[0074] From the equations (11) and (12), the following equation (13) isobtained.

P _(i−1) ² =P _(i) ² −δL _(i,i−1) F _(i,i−1)/(πD _(H) ⁴/4)  (13)

[0075] From the equation (13), the following equation (14) is obtained.

P _(i) ={P _(I−1) ² −δL _(i,i−l) F _(i,i−1)/(πD _(H) ⁴/4 )}^(0.6)  (14)

[0076] Here, F_(i,i−1) in the equation (14) is the gas flow rate in asection in the duct that is adjacent to the ith hole, and is expressedby the following equation (15).

F _(i,i−1) =F ₀/2−F ₁/2−(F ₂ +F ₃ +. . .+F _(i−1))  (15)

[0077] The equation (15) is substituted in the equation (14) to obtainthe following equation (16), which expresses the duct inner pressure P₁below the ith hole by the flow rate of a hole that is situated at alower side of the ith hole.

P ₁ =[P _(i−1) ² +δL _(i,i−1) {F ₀/2−F ₁ /c−(F ₂ +F ₃ +. . .+F_(i−1))}/(πD _(H) ⁴/4)]^(0.5)   (16)

[0078] From the above equations, a desired exhaust flow rate can bedetermined for each hole starting from the downstream side. By thismethod, the gas flow rate of each hole can be detected, so that theuniformity of the porous baffle plate can be detected.

[0079] Using this technique, the uniformity of the exhaust flow ratewith a conventional baffle plate is calculated for a comparison purpose.If the number of holes, the pore size, the hole interval, and the platethickness are known, the uniformity of the exhaust flow rate of theporous baffle plate is determined as follows. First, the duct innerpressure P₁ below the first hole is assumed, and the flow rate F₁ isdetermined from the pore size D₁ and the duct inner pressure P₁ of thefirst hole. The inner pressure P₂ and the flow rate F₂ of the secondhole are then calculated, and the flow rates of all the remaining holesare calculated in order. The duct inner pressure P₁ of the first holeshould be determined so that the total of the exhaust flow rate of allthe holes becomes equal to the flow rate F₀ [sccm] of the process. Thiscalculation should be easily made using spreadsheet software. The unit[sccm] is the amount of gas (cm³) that flows per minute in a normalstate.

[0080] Without using the technique of determining the shape of a baffleplate based on the relational expressions in accordance with the presentinvention, it is difficult to determine a satisfactory shape byrepeating the measurement of the flow rate variation of test baffleplates. It is also difficult to determine the shape of a baffle plate bya fluid simulation method using a computer, because repeatingtrial-and-error simulations by inputting an unlimited number ofparameters for shape determination without any analytical barometers isnot very efficient.

[0081] Accordingly, by the method of the present invention, the shapeand size of required baffles for uniform exhaust can be analyticallydetermined, and such baffles can be efficiently produced.

[0082]FIG. 3 shows the structure of a conventional baffle plate, andFIG. 4 shows the structure of the gas processing chamber 15 providedwith the baffle plate 9 shown in FIG. 3. Here, an exhaust pump P isconnected to the gas processing chamber 15 so as to form a gasprocessing device.

[0083] As shown in FIG. 3, the baffle plate 9 are provided with thebaffle holes 7 having the same pore size and formed on the circumferenceat uniform intervals. If the baffle plate 9 having such a structure isemployed, a gas supplied from a gas introduction pipe 17 into the wafer1 via a shower head 14 is discharged through the baffle hole 7 in thevicinity of the connecting port of the exhaust pipe 1 connected to theexhaust pump P. As a result, the exhaust in the circumferentialdirection of the wafer 1 has a poor uniformity. On the other hand, ifthe pore size of each baffle hole 7 is made smaller, the uniformity canbe improved. However, the pore size of each baffle hole 7 cannot be madevery small in view of the upper limit of the process pressure.

[0084] The uniformity of the exhaust flow rate in the circumferentialdirection of a wafer in a case where a conventional baffle plateprovided with baffle holes having uniform pore sizes, uniformthicknesses, and uniform intervals is employed is shown in Table 1 forreference. In Table 1, “uniformity” can be determined by calculating(maximum flow rate−minimum flow rate)/(maximum flow rate+minimum flowrate) from the maximum value and the minimum value of the flow rate ofeach baffle hole. If the “uniformity” value becomes greater, the flowrates of the baffle holes become more uneven. As the “uniformity” valuebecomes smaller, the flow rates of the baffle holes become more uniform.TABLE 1 PORE SIZE mm 5.0 4.0 3.0 2.5 2.444 2.0 1.0 MINIMUM FLOW RATEsccm 2.6 6.9 12.2 14.3 14.5 8.0 0.591 MAXIMUM FLOW RATE sccm 62.0 41.026.1 21.5 21.3 9.6 0.598 MAX/MIN % 23.7 6.0 2.1 1.50 1.47 1.2 1.01 FLOWRATE UNIFORMITY % 91.9 71.2 36.1 20.1 19.0 9.1 0.6 EXHAUST % 100 100 100100 100 51 3.6 LOWEST DUCT PRESSURE Pa 85.3 79.9 63.6 27 6.67 6.67 6.67

[0085] Table 1 shows data in a case where a porous baffle plate having athickness of 1 mm is placed on an exhaust duct having a width of 25 mm,a depth of 30 mm, and a pitch circle radius of 120 mm in a singletungsten CVD apparatus. Seventy-two baffle holes having uniform poresizes are placed on the pitch circle at uniform intervals at every 5degrees. Using this apparatus, a CVD process gas having an exhaust totalflow rate F₀ of 1203 sccm was processed. The baffle hole pore sizes are5 mm, 4 mm, 3 mm, 2.5 mm, 2.444 mm, 2 mm, and 1 mm, and calculatedvalues are shown for each pore size. Under the processing conditions,the pressure ⁰P in the chamber on the upstream side of the baffle holes7 is 93.3 Pa, the temperature T is 520° C., the average molecular weightof the gas is 0.0596 kg/mol, the viscosity μ is 3.625E-5Pa·sec, and thelimit of the suction pressure of the exhaust outlet is 6.67 pa.

[0086] As shown in Table 1, the exhaust flow rate is 12.2 sccm at thesmallest and 26.1 sccm at the largest with relatively small baffle holeseach having a pore size of 3 mm. The exhaust uniformity obtained bycalculating the (maximum flow rate−minimum flow rate)/(maximum flowrate+minimum flow rate) is 36.1%, which is a poor value. The maximumflow rate is obtained at the baffle hole closest to the exhaust outlet.The duct inner pressure immediately below the baffle hole closest to theexhaust outlet is 63.6 Pa at the smallest, where the differentialpressure with the chamber pressure of 93.3 Pa is 29.7 Pa, which is thelargest. Since the duct inner pressure becomes higher at a locationfurther away from the exhaust outlet, the differential pressure with thechamber inner pressure becomes lower at such a location. Accordingly,the exhaust flow rate becomes the smallest at a location furthest fromthe connecting port of the exhaust pipe 11.

[0087] As shown in Table 1, the exhaust uniformity becomes poorer with alarger pore size. On the other hand, the exhaust uniformity improveswith a smaller pore size. However, with a small pore size, it isnecessary to reduce the duct inner pressure, because a largedifferential pressure is required for exhausting the gas at apredetermined flow rate with a small pore size. In this example, theuniformity value with the pore size of 2.444 mm can maintain the uniformvalue of 19.0%. With the smaller pore sizes of 2.0 mm and 1.0 mm, theexhaust becomes too low. For instance, to maintain the same chamberpressure with the pore size of 2.0 mm, the exhaust gas flow rate needsto be reduced to 51%.

[0088] In the following, the five types of suitable baffle plates willbe described.

[0089] [Embodiment 1]

[0090] In a first embodiment of the present invention, a porous baffleplate having uniform hole pore sizes and uniform thicknesses for uniformexhaust with a varying pitch between baffle holes.

[0091] The porous baffle plate of this embodiment has baffle holes eachhaving the same pore size. However, the intervals between the baffleholes are varied to maintain the average exhaust flow rate uniform inthe circumferential direction.

[0092]FIG. 5 illustrates the arrangement of baffle holes 23 formed in abaffle plate 21 of the first embodiment. As shown in FIG. 5, theinterval between each two baffle holes 23 on the downstream side, whichis close to the connecting port of the exhaust pipe, is wider than onthe upstream side, taking into account an increase of the exhaust flowrate of each baffle hole due to an excessive differential suctionpressure. The arrangement of the hole intervals necessary to make theaverage exhaust flow rate uniform on the circumference is as follows.

[0093] A location at the angle of circumference of the ith hole is θ_(i)degrees, with the connecting port of the exhaust pipe being the origin,as shown in FIG. 5. In the following description, the first hole h1 islocated at the same angle of circumference as the exhaust port, i.e.,θ₁=0°. However, the arrangement of this embodiment can be used in othersituations. The flow rate of the exhaust gas passing through the ithholes is F_(i) [sccm], and the duct inner pressure below the ith hole isP_(i) [Pa]. The equivalent diameter D_(H) [m], the thickness of thebaffle plate is L₀ [m], the radius of the pitch circle 19 of the hole isr [m], the total exhaust flow rate is F₀ [sccm], the pressure of theprocessing chamber is ⁰P [Pa]. The angle of the circumferential angleregion in which the ith hole is ±α₁ degrees. Here, the followingequations hold.

θ₁=0  (17)

F ₁=(⁰ P ² −P ₁ ²)(πD ₀ ⁴/4)/δL ₀  (18)

α₁=(180)F ₁ /F ₀  (19)

θ₂=(α₁+180 F ₁ /F ₀)/{1+(1−F ₁ /F ₀) (πr/2L ₀)(D ₀ /D _(H))⁴}  (20)

F ₂=(θ₂−α₁)F ₀/180  (21)

α₂=(180)F ₂ /F ₀=θ₂−θ₁−α₁  (22)

P ₂ =[P ₁ ²+(δrθ ₂(F ₀ −F ₁)/360)/{(1/4)D _(H) ⁴}]^(0.5)   (23)

δ=(64 μRT)(1E·6/60)(1/0.0224)  (24)

[0094] Generally, with i being greater than 2, the following equationshold.

θ_(i)={θ_(i−1)+α_(i−1)+180 F _(i−1) /F ₀+(πr/L ₀ F ₀) (F ₀/2−F ₁/2F ₂ −.. .−F _(i−1))(D ₀ /D _(H))⁴θ_(i−1)}/{1+(rπ/L ₀ F ₀)(F ₀/2−F ₁/2−F ₂ 31 F₁ −. . . −F _(i−1)) (D ₀ /D _(H))⁴}  (25)

α_(i)=θ_(i)−θ_(i−1)−α_(i−1)  (26)

F _(i)=α_(i) F ₀/180=(⁰ P ¹ −P _(i) ²) (πD ₀ ⁴/4)/δL ₀  (27)

P _(i)=[⁰ P ² −δL ₀ F _(i)/(πD ₀ ⁴/4)]^(0.5) =[P _(i−1) ²÷(δL _(i,i−1) F_(i,i−1))/(πD _(H) ⁴ /4)] ^(0.5)  (28)

[0095] The flow rate F₁ of the first hole h1 with respect to the ductinner pressure P₁ below the first hole h1 is determined, and the angleα₁ on one side of the exhaust region of the first hole h1 based on theflow rate F₁. The angle position θ₂ of the second hole h2 is calculatedbased on the flow rate F₁ and the angle α₁, and the flow rate F₂ of thesecond hole h2 is determined from the angle position θ₂ and the angleα₁. The angle α₂ is then obtained from the flow rate F₂. The duct innerpressure P₂ of the second hole h2 is calculated as the functions ofthese elements. As for the third hole and the remaining holes, the samecalculations are made so as to determine the variation of the anglepositions of all the exhaust holes that are given a uniform exhaust flowrate per unit circumferential angle. The initial pressure P₁ isconverted so that the total of the obtained flow rates satisfies theconditions of the process gas flow rates. Thus, the variation of theangle position θ_(i) of each hole can be obtained.

[0096]FIG. 6 shows the baffle plate 21 of the first embodiment in whichthe baffle holes 23 are formed at the angle positions θ₁ obtained in theabove manner.

[0097] If the first hole h1 or the nth hole hn is located on thestraight line between 0° and 180° on the pitch circle 19, a coefficientc₁ or c_(n) mentioned later is 2. If the first hole h1 or the nth holehn is not located on the straight line, the coefficient c₁ or c_(n)mentioned later is 1. In a case where the total number m of holes is 72and the coefficient c₁ of cn is 2, n is determined to be 37 by (m+2)/2.The total exhaust flow rate F₀ is determined as follows.

F ₀ =2( F ₁ /c ₁ +F ₂ +F ₃ +. . .+F _(n-1) +F _(n) /c _(n))  (29)

[0098] In the following, eight aspects of the baffle plate 21 havingbaffle holes arranged at varied intervals so as to obtain uniformexhaust will be described.

[0099] (Standard Conditions)

[0100] Under the same process conditions as with the conventional baffleplate shown in FIG. 3, the uniform exhaust test was carried out with thebaffle plate 21 having the baffle holes arranged at the optimumintervals on the pitch circle 19. The pore sizes were 2.5 mm, 3 mm, 4mm, and 5 mm. The number of holes was 72. Table 2 shows the relationshipbetween the optimum variation and the pore size between 0° to 180° ofeach hole. TABLE 2 ANGLE PORE SIZE HOLE NUMBER PORE SIZE HOLE NUMBER 2.5mm 3.0 mm 4 mm 5 mm ANGLE 2.5 mm 3.0 mm 4 mm 5 mm  1 0.0 0.0 0.0 0.0  26.6 8.4 16.6 32.9 20 104.7 113.3 135.9 154.9  3 13.0 16.5 30.7 55.9 21109.4 117.6 139.1 156.8  4 19.3 24.1 43.0 73.0 22 114.0 121.9 142.1158.7  5 25.4 31.3 53.7 86.2 23 118.6 126.1 145.1 160.4  6 31.4 38.363.2 96.7 24 123.2 130.2 147.9 162.1  7 37.3 44.9 71.6 105.3 25 127.7134.3 150.7 163.7  8 43.0 51.3 79.2 112.6 26 132.1 138.3 153.4 165.2  948.7 57.4 86.1 118.7 27 136.6 142.2 156.0 166.7 10 54.2 63.3 92.4 124.128 141.0 146.1 158.8 168.2 11 59.6 69.0 98.2 128.7 29 145.4 150.0 161.1169.6 12 64.9 74.5 103.6 132.8 30 149.8 153.8 163.5 171.0 13 70.2 79.9108.5 136.5 31 154.1 157.6 166.0 172.3 14 75.3 85.0 113.1 139.9 32 158.5161.4 168.3 173.6 15 80.4 90.0 117.5 142.9 33 162.8 165.1 170.7 174.9 1685.4 94.9 121.6 145.7 34 167.1 168.9 173.0 176.2 17 90.3 99.7 125.4148.2 35 171.4 172.6 175.4 177.5 18 95.1 104.3 129.1 150.6 36 175.7176.3 177.7 178.7 19 99.9 108.8 132.6 152.8 37 180.0 180.0 180.0 180.0

[0101] As shown in Table 2, the interval between the first hole h1 andthe second hole h2 is the largest with each pore size, while theinterval between the 36th hole and the 37th hole on the 180° sidebecomes the smallest. Table 3 shows the relationship between theuniformity of the baffle plate having varied hole intervals and theprocess conditions. TABLE 3 COLUMN NUMBER 1-1 1-2 1-3 1-4 1-5 CHAMBERPRESSURE Pa 93.3 133.3 93.3 93.3 93.3 TOTAL GAS FLOW RATE sccm 1203 1203601.5 1203 1203 TEMPERATURE ° C. 520 520 520 600 520 GAS VISCOSITY Pa ·s 3.63E − 05 3.63E − 05 3.63E − 05 3.63E − 05 1.5 × 3.63E − 05 PORE SIZEmm 3 3 3 3 3 DUCT EQUIVALENT DIAMETER mm 27.3 27.3 27.3 27.3 27.3 NUMBERof HOLES (ON THE 72 72 72 72 72 ENTIRE CIRCUMFERENCE) HOLE NUMBER No. 137 1 37 1 37 1 37 1 37 HOLE INTERVALS deg 8.445 3.708 8.445 3.708 8.4453.708 8.445 3.708 8.445 3.708 DIFFERENTIAL SUCITON Pa 33.9 12.7 21.1 8.615.1 6.1 38.5 14.1 62.8 19.9 PRESSURE DUCT INNER PRESSURE Pa 59.4 80.6112.2 124.7 78.2 87.2 54.8 79.2 30.5 73.4 FLOW RATE PER HOLE sccm 28.9812.39 28.98 12.39 14.49 6.19 28.98 12.39 28.98 12.39 FLOW RATE PER UNITANGLE sccm 3.342 3.342 3.342 3.342 1.671 1.671 3.342 3.342 3.342 3.342UNIFORMITY (m.m. METHOD) % 0.00% 0.00% 0.00% 0.00% 0.00%

[0102] The differential suction pressure shown in Table 3 indicates thedifference between the inner pressure of the process chamber at eachbaffle hole 23 and the inner pressure of the exhaust duct.

[0103] The case of the 3-mm pore size in Table 2 corresponds to thecolumn 1-1 in Table 3. In the case of the column 1-1, the maximuminterval between the baffle holes 23 is 8.4 degrees between the firsthole h1 and the second hole h2, and the minimum interval is 3.7 degreesbetween the 36th hole and the 37th hole. The maximum flow rate is 29sccm at the first hole h1, and the minimum flow rate is 12.4 sccm at the37th hole. The values obtained by dividing the flow rate of the baffleholes 23 by the angle 2 α₁ and 2 α₃₇ of the exhaust region with respectto each baffle hole 23 are equivalent to the flow rate per one degreeshown in the column 1-1 in Table 3. The values are both 3.342 sccm. Asfor the other baffle holes 23 at the other positions, the flow rate ofthe exhaust gas of each hole is divided by the angle of the exhaustregion, and the average exhaust flow rates per unit circumferentialangle are the same. Thus, the uniformity value is 0%.

[0104] The positions of the baffle holes 23 are shown withcircumferential angles in the range of 0° to 180°, with the position ofthe connecting port of the exhaust pipe 11 being the origin. The firsthole h1 among the 72 holes on the pitch circle 19 is located at 0°, andthe 37th hole is located at 180°. The second hole h2 to the 36th holeare located at the angles shown in Table 3, but the 38th to 72nd holesare located on the circumference on the opposite side of the origin, andarranged symmetrically with the locations of the second hole h2 to the36th hole with respect to the line between 0° and 180°.

[0105] Also, in the case of the column 1-1 in Table 3, the duct innerpressure immediately below the first hole h1 is 59.4 Pa, which isslightly lower than the lowest duct inner pressure of 63.6 Pa in thecase of a pore size of 3 mm shown in Table 1. However, the intervalsbetween the baffle holes 7 in the conventional baffle plate 9 shown inFIG. 1 is uniform. On the other hand, the intervals between the baffleholes 23 in the baffle plate 21 of this embodiment varies in the rangeof 3.7 to 8.4 degrees as shown in the column 1-1 in Table 3, so that thevariation of the exhaust flow rate per unit circumferential angle isaveraged. As result, the uniformity approaches 0%. This proves that theuniformity is dramatically improved, compared with the conventionalbaffle plate shown in Table 1.

[0106] (Influence of Pressure Variations)

[0107] Using the baffle plate 21 of the first embodiment, the exhaustgas can be evenly distributed in the circumferential direction even ofthe chamber inner pressure varies. Under the same process conditions asshown in the column 1-1 in Table 3, except that the chamber innerpressure was 133.3 Pa, the locations of the 72 baffle holes each havinga pore size of 3 mm were determined so that the exhaust from the chamberis distributed evenly in the circumferential direction. The results ofthis were exactly the same as the values in the case of the pore size of3 mm shown in Table 2, as shown in the column 1-2 in Table 3.Accordingly, it was confirmed that the inner pressure of the gas processchamber had no adverse influence on the optimum hole intervals foruniform exhaust.

[0108] The lowest exhaust pressure immediately below the first hole h1needs to be adjusted to 112.2 Pa, because the lowest exhaust pressureshould correspond to a chamber pressure that is higher than the chamberpressure in the column 1-1 in Table 3. Thus, the inner pressure of theprocess chamber is maintained at 133.3 Pa.

[0109] (Influence of Flow Rate Variations)

[0110] Using the baffle plate shown in the column 1-1 in Table 3, thevariation of the exhaust flow rate in the circumferential direction canbe made uniform. Under the same process conditions as in the column 1-1of Table 3, except that the total flow rate of the gas exhaust was 601.5sccm, which is a half of the total flow rate in the column 1-1 of Table3, the locations of the baffle holes required for uniform exhaust weredetermined. The results of this were exactly the same as the values inthe case of the pore size of 3 mm shown in Table 2, as shown in thecolumn 1-3 of Table 3. Accordingly, it was confirmed that the flow rateof the process gas had no adverse influence on the optimum holeintervals for uniform exhaust. However, the lowest exhaust pressureimmediately below the first hole h1 needs to be adjusted to 78.2 Pa soas to accommodate an exhaust flow rate lower than that in the column 1-1of Table 3. By doing so, the exhaust gas can be distributed evenly inthe circumferential direction, while the chamber inner pressure ismaintained at 93.3 Pa. The exhaust flow rate per unit circumferentialangle is reduced as the amount of process gas decreases. However, it wasfound that the exhaust flow rate per unit circumferential angle is aconstant value of 1.671 sccm, regardless of the locations of the holes.

[0111] (Influence of Temperature Variations)

[0112] Using the baffle plate shown in the column 1-1 of Table 3, thevariation of the exhaust flow rate can be made uniform in thecircumferential direction even if the process temperature varies. Underthe same process conditions as in the column 1-1 of Table 3, except thatthe process gas temperature was 600° C., the locations of the baffleholes required for uniform exhaust were determined. The results of thiswere exactly the same as the values in the case of the pore size of 3 mmshown in Table 2, as shown in the column 1-4 of Table 3. Accordingly, itwas confirmed that the process gas temperature had no adverse influenceon the optimum hole intervals for uniform exhaust.

[0113] The lowest exhaust pressure immediately below the first hole h1needs to be adjusted to 54.8 Pa, so as to accommodate an increasedexhaust flow rate due to a higher temperature than in the column 1-1 ofTable 3. By doing so, the exhaust gas can be distributed uniformly inthe circumferential direction, while the chamber inner pressure ismaintained at 93.3 Pa.

[0114] (Influence of Viscosity Variations)

[0115] Using the baffle plate shown in the column 1-1 of Table 3, it wasfound that the exhaust gas can be distributed uniformly in thecircumferential direction even if the gas viscosity varies. Under thesame process conditions as in the column 1-1 of Table 3, except that thegas viscosity is 5.44E-5Pa·s, which is 1.5 times as high as that in thecolumn 1-1 of Table 3, the locations of the baffle holes were againdetermined so that the exhaust from the chamber can be distributeduniformly in the circumferential direction by the 72 baffle holes eachhaving the pore size of 3 mm. The results of this were exactly the sameas the values in the case of the pore size of 3 mm in Table 2, as shownin the column 1-5 of Table 3. Accordingly, it was confirmed that theprocess gas viscosity had no adverse influence on the optimum intervalsfor uniform exhaust.

[0116] However, the lowest exhaust pressure immediately below-the firsthole h1 needs to be adjusted to 30.5 Pa, so as to accommodate anincreased gas viscosity that is higher than that in the column 1-1 ofTable 3. By doing so, the exhaust gas can be distributed uniformly inthe circumferential direction, while the chamber inner pressure ismaintained at 93.3 Pa.

[0117] (Influence of Pore size Variations)

[0118] Table 4 shows the relationship between the uniformity of thebaffle plate having varied hole intervals and the conditions of fluidpassages. TABLE 4 COLUMN NUMBER 1-1 1-6 1-7 1-8 CHAMBER PRESSURE Pa 93.393.3 93.3 93.3 TOTAL GAS FLOW RATE sccm 1203 1203 1203 1203 TEMPERATURE° C. 520 520 520 600 GAS VISCOSITY Pa · s 3.63E − 05 3.63E − 05 3.63E −05 3.63E − 05 PORE SIZE mm 3 2.5 3 3 DUCT EQUIVALENT DIAMETER mm 27.327.3 34.3 27.3 NUMBER of HOLES (ON THE 72 72 72 72 ENTIRE CIRCUMFERENCE)HOLE NUMBER No. 1 37 1 37 1 37 1 37 HOLE INTERVALS deg 8.445 3.708 6.6034.295 6.322 4.403 11.085 6.420 DIFFERENTIAL SUCITON Pa 33.9 12.7 72.935.1 23.4 15.3 49.6 28.8 PRESSURE DUCT INNER PRESSURE Pa 59.4 80.6 20.458.2 69.9 78.0 43.7 64.5 FLOW RATE PER HOLE sccm 28.98 12.39 22.35 14.3521.35 14.71 38.03 25.44 FLOW RATE PER UNIT ANGLE sccm 3.342 3.342 3.3423.342 3.342 3.342 3.342 3.342 UNIFORMITY (m.m. METHOD) % 0.00% 0.00%0.00% 0.00%

[0119] If a baffle plate having 72 holes each having a pore size of 2.5mm, instead of 3 mm, the locations of the baffle holes required foruniform exhaust in the circumferential direction were determined. Theresults of this are shown in the column 1-6 of Table 4. The anglepositions of the baffle holes are shown in the column of the pore sizeof 2.5 mm in Table 2.

[0120] Compared with the case of the pore size of 3 mm, the holeintervals of the 2.5-mm pore size holes exhibit higher uniformity. Sincethe differential suction pressure in the duct immediately below thefirst hole h1 is reduced to 20.4 Pa in the column 1-6 of Table 4, thedifferential pressure between the chamber pressure and the duct innerpressure due to higher fluid friction resistance with the smaller poresize. Accordingly, the differential pressure at each hole becomeshigher. As a result, the influence of a variation of the duct innerpressure in the circumferential direction becomes relatively smaller,and the difference in exhaust flow rate due to the differential suctionpressure between hole locations also becomes smaller. Thus, theintervals between the holes exhibit more uniformity.

[0121] In Table 2, the variations of exhaust are shown in the case ofthe pore sizes of 4 mm and 5 mm, as well as 2.5 mm and 3 mm. Inaccordance with Table 2, as the pore size becomes larger, the holeintervals on the first hole side become longer, while the hole intervalson the 180° side become shorter. However, it is obvious that each poresize should be smaller than the hole intervals.

[0122] (Influence of Variations in Duct Equivalent Diameter)

[0123] Using a baffle plate having the same number of holes with thesame pore size as in the column 1-1 of Table 3, except that theequivalent diameter of the exhaust duct is enlarged from 27.3 mm to 34.3mm, the locations of baffle holes were again determined so that uniformexhaust of exhaust gases of the same flow rate, the same pressure, andthe same temperature can be obtained in the circumferential direction.The results of this are shown in the column 1-7 of Table 4.

[0124] Since the fluid friction resistance in a wider duct is smaller,the differential pressure required for drawing gas from the chamber intothe duct becomes more uniform. As a result, the intervals between thebaffle holes for obtaining uniform exhaust per unit angle in thecircumferential direction also become more uniform than in the case ofthe column 1-1 of Table 3.

[0125] (Influence of Variations in Hole Number)

[0126] Under the same conditions as in the column 1-1 of Table 3, exceptthat the number of baffle holes is 47 instead of 72, the locations ofthe baffle holes required for obtaining uniform exhaust in thecircumferential direction were determined. The results of this are shownin the column 1-8 of Table 4. The angle locations of the baffle holescan be determined in the same manner as described so far.

[0127] As the number of holes decreases, the maximum hole intervals andthe minimum hole intervals both increase, and the flow rate of each holealso becomes higher. However, the exhaust flow rate per unitcircumferential angle is constantly 3.342 sccm, regardless of thelocations of the holes. From this fact, it becomes apparent that thetechnique of obtaining uniform exhaust by varying the hole intervals canbe applied to a case in which the number of holes varies.

[0128] [Second Embodiment]

[0129] A second embodiment of the present invention shows a case where aporous baffle plate has baffle holes arranged at uniform intervals andhaving different pore sizes for obtaining uniform exhaust. In thisporous baffle plate, the hole intervals and the thickness are uniform,but the pore sizes are varied so that a uniform exhaust flow rate can bemaintained in the circumferential direction.

[0130]FIG. 7 shows the structure of the baffle plate of the secondembodiment of the present invention. As shown in FIG. 7, the pore sizeis smaller on the downstream side in the vicinity of the connecting portof the exhaust pipe 11, so as to restrict an increase of the exhaustflow rate of each hole due to an excessive differential suctionpressure. In order to obtain a uniform flow rate, the pore sizes aredesigned in the following manner.

[0131] A method of determining the optimum pore size variation of mbaffle holes 27 arranged on the pitch circle 19 at uniform intervalswill now be described. The exhaust flow rate per hole is the averageflow rate, i.e., F_(m)=F₀/m. The pore size D₁ of the hole located at themost downstream side is arbitrarily given as the minimum design poresize, so that the other pore sizes can be determined from therelationship described below.

[0132] The relationship between the pore size D₁ and the flow rate F₁ ofthe first hole can be expressed by the differential pressure Δ⁰P₁(=⁰P−P₁) between the duct inner pressure P₁ and the chamber pressure ⁰Pas follows.

F ₁=(⁰ P ² −P ₁ ²){(π/4)D ₁ ⁴ }/δL ₀ =F _(m) =F ₀ /m  (30)

[0133] From the above equation, the duct inner pressure can bedetermined by the following equation (31).

P ₁={⁰ P ² −δL ₀ F ₀/(πmD ₁ ⁴/4)}^(0.5)  (31)

[0134] The duct inner pressure P₂ immediately below the second hole ishigher than the duct inner pressure P₁ by the differential pressureΔP_(2,1), and can be determined by the relationship with the massvelocity G_(2,1) (=F_(2,1) (1E-6/60)(M/0.0224)/((π/4)D_(H) ²)) of thegas F_(2,1) (=(F₀−F₁)/2) flowing the distance of the duct length L_(m)(=2πr/m).

P ₂ =[P ₁ ² +{δL _(m)(F ₀/2−F ₁/2) /{(π/4)D _(H) ⁴}]^(0.5)  (32)

[0135] From this equation, the pore size D₂ having the flow rate F₂ ofthe second hole as the uniform flow rate F_(m) can be obtained. As forthe other baffle holes, the pore sizes are determined in the samemanner.

F ₂=(⁰ P ² −P ₂ ²){(π/4)D ₂ ⁴ }/δL ₀ =F ₀ /m  (33)

D ₂ =[δL ₀ F ₀/{(πm/4)⁰ P ² −P ₂ ²)}]^(1/4)  (34)

[0136] As for the ith hole, the following equations hold.

P _(i)=[⁰ P ² δL ₀ F _(i)/{(π/4)D _(i) ⁴}]^(0.5)  (35)

P _(i) =[P _(i−1) ² +{δL _(m)(F ₀/2−F ₁/2−F ₂ −. . . −F ¹⁻¹) /{(π/4)D_(H) ⁴}]^(0.5)  (36)

F _(i)=(⁰ P ² −P _(i) ²){(π/4)D _(i) ⁴ }/δL ₀ =F ₀ /m  (37)

D _(i) =[δL ₀ F ₀/{(πm/4)(⁰ P ² −P _(i) ²) }]^(1/4)  (38)

[0137] The relational expression (36) with respect to i and i−i is thensubstituted in the equation (35) as follows.

[⁰ P ² −δL ₀ F _(i)/{(π/4)D _(i) ⁴}]^(0.5)=[⁰ P ² −δL ₀ F _(i−1)/{(π/4)D_(i−1) ⁴ }+{δL _(m)(F ₀/2−F ₁/2−F ₂ −. . .−F _(i−1))/{(π/4) D _(H)⁴}]^(0.5)  (39)

[0138] By arranging this equation, the following equation (40) isobtained.

D _(i) ⁴ /D _(i−1) ⁴−{(2πr/mL ₀){(F ₀/2−F ₁/2−F ₂ −. . .−F _(i−1))/F_(i−1)}(D _(i) ⁴ /D _(H) ⁴)=F _(i) /F _(i−1)  (40)

[0139] When the flow rates of the holes are uniform, the right-hand sideof the equation (40) becomes 1. Accordingly, the following equationshold.

D _(i) ⁴ /D _(i−1) ⁴−{(πr/mL ₀)(m+3−2i) (D _(i) ⁴ /D _(H) ⁴)=1  (41)

D _(i) ⁴[1/D _(i−1) ⁴{(πr/mL ₀ D _(H) ⁴)(m+3−2i) }]=1  (42)

D _(i)=1/[1/D _(i−1) ⁴−{(πr/mL ₀ D _(H) ⁴) (m+3−2i)}]^(1/4)  (43)

[0140] When the pore size of each hole satisfies the relationalexpression (43), the flow rates of the holes are apparently uniform.

[0141] As described above, the diameter of each of the baffle holes 27arranged at uniform intervals can be determined by the equation (43).Accordingly, it became apparent that the pore size of each baffle hole27 depends on only the number m of holes, the plate thickness L₀, thepitch circle radius r, and the duct effective diameter D_(H), but not onthe total flow rate F₀, the chamber pressure ⁰P, the temperature T, andthe viscosity. The diameter D₁ of the first hole is given as thereference value, so that the duct inner pressure P₁ to maintain thechamber pressure ⁰P with respect to the total flow rate F₀ can becalculated by the equation (31). The duct inner pressure P₁ thusobtained is important to adjust the pressure of the exhaust system.

[0142] Table 5 shows the relationship between the pore size and thesuction pressure in the exhaust baffle plate 25 having the baffle holeshaving different diameters. TABLE 5 COLUMN NUMBER 2-1 2-2 2-3 2-4CHAMBER PRESSURE Pa 93.3 ← ← ← TOTAL GAS FLOW RATE sccm 1203 ← ← ←TEMPERATURE ° C. 520 ← ← ← GAS VISCOSITY Pa · s 3.63E − 05 ← ← ← HOLEINTERVALS UNIFORM ← ← ← NUMBER of HOLES (ON THE 72 ← ← ← ENTIRECIRCUMFERENCE) BAFFLE PLATE THICKNESS mm 1 ← ← ← DUCT EQUIVALENTDIAMETER mm 27.3 ← ← ← PITCH CIRCLE DIAMETER mm 240 ← ← ← SMALL- LARG-SMALL- LARG- SMALL- LARG- SMALL- LARG- EST EST EST EST EST EST EST ESTHOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE DORE SIZE D: mm 2.30 2.56 2.402.73 2.50 2.94 2.60 3.19 DIFFERENTIAL SUCITON Pa 85.5 38.3 55.8 27.143.2 19.3 34.9 13.4 PRESSURE ΔOPI DUCT INNER PRESSURE Pi Pa 7.8 55.137.6 66.2 50.1 74.0 58.4 79.9 FLOW RATE PER HOLE Fi sccm 16.7 16.7 16.716.7 16.7 16.7 16.7 16.7 UNIFORMITY (m.m. METHOD) % 0.00% 0.00% 0.00%0.00% COLUMN NUMBER 2-5 2-6 CHAMBER PRESSURE Pa ← ← TOTAL GAS FLOW RATEsccm ← ← TEMPERATURE ° C. ← ← GAS VISCOSITY Pa · s ← ← HOLE INTERVALS ←← NUMBER of HOLES (ON THE ← ← ENTIRE CIRCUMFERENCE) BAFFLE PLATETHICKNESS mm ← ← DUCT EQUIVALENT DIAMETER mm ← ← PITCH CIRCLE DIAMETERmm ← ← SMALLEST LARGEST SMALLEST LARGEST HOLE HOLE HOLE HOLE DORE SIZED: mm 2.80 3.97 3.00 10.52 DIFFERENTIAL SUCITON Pa 24.3 5.4 17.7 0.1PRESSURE ΔOPI DUCT INNER PRESSURE Pi Pa 69.1 88.0 69.1 88 FLOW RATE PERHOLE Fi sccm 16.7 16.7 75.6 16.7 UNIFORMITY (m.m. METHOD) % 0.00% 0.00%

[0143] Table 5 shows data concerning the porous baffle plate providedwith baffle holes 27 that are arranged at uniform intervals on the pitchcircle and have various diameters, under the same process conditions asthe process conditions in obtaining the data shown in Table 1. In Table5, only the maximum pore size and the minimum pore size among the 72baffle holes formed in the baffle plate are shown. However, the otherholes are formed to satisfy the equation (43).

[0144] The columns 2-1 to 2-6 of Table 5 shows the results ofexperiments on the minimum pore size in the range of 2.3 mm to 3 mm ofthe baffle holes 27. From these results, it is confirmed that theexhaust flow rate per hole is the same regardless of the pore size.

[0145] Also, the differential pressure between the two sides of eachbaffle hole 27 becomes larger, as the pore size becomes smaller.However, in the column 2-1 of Table, the minimum pore size is 2.3 mm,while the maximum pore size is only 2.56 mm. Accordingly, it is notnecessary to vary the pore sizes in a wide range. In this case, however,it is necessary to reduce the inner pressure of the first hole to 7.8Pa, which is close to 6.67 Pa, the limit of the suction pressure. In acase where the baffle plate 25 is employed, the gas flow load cannot beincreased any further. Meanwhile, in the case of the column 2-6 of Table5, the minimum pore size is 3 mm, while the maximum pore size needs tobe as large as 10.5 mm. This maximum pore size is almost the same as theaverage hole interval (240 π/72=10.47 mm), and also the upper limit ofthe pore size. The duct inner pressure below the baffle hole 27 havingthe largest pore size is almost as large as 93.3 Pa, which is equivalentto the inner pressure of the process chamber. Also, the variation of thepore size is a limit, since a uniform suction operation is performed ata very small differential pressure via the baffle hole 27 having thelargest pore size. In these experiments, the baffle plate 25 having thepore size variation shown in the columns 2-2 to 2-5 in Table 5. Asdescribed above, in order to obtain uniform exhaust under desiredprocess conditions, various pore size variations may exist for a porousbaffle plate having a desired number of baffle holes arranged at uniformintervals and a desired thickness. These variations can be easilyembodied by the above relational expressions in accordance with thepresent invention. Furthermore, the baffle plate 25 having the optimumpore size variation for the conditions of the actual processingapparatus.

[0146] Table 6 shows that the exhaust uniformity in the baffle plate 25having a fixed pore size variation does not depend on the processconditions. TABLE 6 COLUMN NUMBER 2-4 2-7 2-8 2-9 CHAMBER PRESSURE Pa93.3 133.3 93.3 93.3 TOTAL GAS FLOW RATE sccm 1203 1203 600 900TEMPERATURE ° C. 520 520 520 520 GAS VISCOSITY Pa · s 3.63E − 05 3.63E −05 3.63E − 05 3.63E − 05 HOLE INTERVALS UNIFORM UNIFORM UNIFORM UNIFORMNUMBER of HOLES (ON THE 72 72 72 72 ENTIRE CIRCUMFERENCE) BAFFLE PLATETHICKNESS mm 1 3 3 3 DUCT EQUIVALENT DIAMETER mm 27.3 27.3 27.3 27.3PITCH CIRCLE DIAMETER mm 240 240 240 240 SMALL- LARG- SMALL- LARG-SMALL- LARG- SMALL- LARG- EST EST EST EST EST EST EST EST HOLE HOLE HOLEHOLE HOLE HOLE HOLE HOLE DORE SIZE D: mm 2.60 3.19 2.60 3.19 2.60 3.192.60 3.19 DIFFERENTIAL SUCITON Pa 34.9 13.4 21.6 9.0 15.4 6.4 24.4 9.9PRESSURE Δ ° Pi DUCT INNER PRESSURE Pi Pa 58.4 79.9 111.7 124.3 77.986.9 68.9 83.5 FLOW RATE PER HOLE Fi sccm 16.7 16.7 16.7 16.7 8.33 8.3312.5 12.5 UNIFORMITY (m.m. METHOD) % 0.00% 0.00% 0.00% 0.00% COLUMNNUMBER 2-10 2-11 CHAMBER PRESSURE Pa 93.3 93.3 TOTAL GAS FLOW RATE sccm1200 1800 TEMPERATURE ° C. 520 520 GAS VISCOSITY Pa · s 3.63E − 05 3.63E− 05 HOLE INTERVALS UNIFORM UNIFORM NUMBER of HOLES (ON THE 72 72 ENTIRECIRCUMFERENCE) BAFFLE PLATE THICKNESS mm 3 3 DUCT EQUIVALENT DIAMETER mm27.3 27.3 PITCH CIRCLE DIAMETER mm 240 240 SMALLEST LARGEST SMALLESTLARGEST HOLE HOLE HOLE HOLE DORE SIZE D: mm 2.60 3.19 2.60 3.19DIFFERENTIAL SUCITON Pa 34.8 13.4 65.4 21.0 PRESSURE Δ ° Pi DUCT INNERPRESSURE Pi Pa 58.5 79.9 28.0 7.23 FLOW RATE PER HOLE Fi sccm 16.7 16.725.0 25.0 UNIFORMITY (m.m. METHOD) % 0.00% 0.00%

[0147] Table 6 shows that a change in the process conditions has noinfluence on the optimum pore size variation in a baffle plate having aminimum pore size of 2.6 mm (shown in the column 2-4 of Table 5). Morespecifically, the flow rates at the baffle hole having the minimum poresize and at the baffle hole having the maximum pore size show that theexhaust flow rate at each of the baffle holes can be uniformlymaintained by simply adjusting the exhaust duct inner pressure P_(i)under the first hole with a change of the process pressure from 93.3 Pato 133.3 Pa as shown in the column 2-7 of Table 6 and a change of theflow load from 600 sccm to 1800 sccm as shown in the columns 2-8 to 2-11of Table 6.

[0148] As can be seen from Table 6, the baffle plate 25 provided withthe baffle holes 27 having different pore sizes from each other is moreadvantageous than the baffle plate 9 having uniform-size baffle holes atuniform intervals shown in Table 1. With the baffle plate 9 shown inTable 1, even if each pore size is 2.444 mm, which makes thedifferential suction pressure so large as to reach the limit of theexhaust capacity, the exhaust uniformity cannot exceed 19.0%. With thebaffle plate 25 having the optimum pore size variation, on the otherhand, uniform exhaust can be constantly obtained in a range in which theduct inner pressure can be adjusted.

[0149] In a case where the pore size of a baffle hole 27 is too small,the differential pressure of the baffle hole 27 increases to restrictthe process gas flow rate and the freedom of the control valves used forpressure control in processes. On the other hand, in a case where thepore size of each baffle hole 27 is too small, the inner pressure in aduct far away from the connecting port of the exhaust pipe 11 becomessubstantially the same as the chamber inner pressure, resulting inundesired exhaust. Accordingly, in order to obtain uniform exhaust, abaffle plate 25 having the optimum pore size variation needs to beselected. This should be easily achieved by the method in accordancewith the present invention.

[0150]FIG. 8 is a graph showing the characteristics of the baffle plate25 of the second embodiment provided with the baffle holes havingdifferent pore sizes from each other. The graph is the results of asimulation in which the total number of holes on a predeterminedcircumference was 72, the hole intervals are uniform, the duct radiuswas 120 mm, the long side of the duct section was 30 mm, the short sideof the duct section was 24 mm, the thickness of the baffle plate was 1mm, the chamber pressure was 93.3 Pa, the gas amount was 1203 sccm, thetemperature was 520° C., the average molecular weight was 59.6 g/mol,and the gas viscosity was 3.625E-5 Pa·sec.

[0151] As shown in FIG. 8, if the first baffle hole 27 (number 1) isformed immediately above the connecting port of the exhaust pipe 11 inthe baffle plate 25 of the second embodiment of the present invention,the pore size D_(i) increases along the semicircle toward the 37thbaffle hole 27 formed on the upstream side. As shown in FIG. 8, in thisbaffle plate 25, the change of the duct inner pressure P_(i) [Pa] withthe hole number is similar to the change with pore size. The duct innerpressure P₁ [Pa] increases from the first baffle hole to the 37th bafflehole. The flow rate F_(i) [sccm] is constant, regardless of the locationof the, as shown in FIG. 8.

[0152]FIG. 9 is a graph showing the results of a simulation performed onthe conventional baffle plate 9 shown in FIG. 3 under the sameconditions as in the case shown in FIG. 8. As shown in FIG. 9, thebaffle plate 9 has baffle holes 7 having uniform pore sizes. The ductinner pressure has a larger increase rate with the hole number, comparedwith the baffle plate 25 of the second embodiment. The flow rate of thegas flowing through the first to 37th baffle holes 7 forms a decreasingfunction with the hole number. Accordingly, the flow rate varies fromthe location of the baffle hole corresponding to the exhaust outlet, anduniform exhaust cannot be realized.

[0153]FIG. 10 is a graph showing the results of a simulation performedon a conventional baffle plate disclosed in Japanese Laid-Open PatentApplication No. 63-141318 under the same conditions as in the case shownin FIG. 8. As shown in FIG. 10, in this baffle plate, the pore size of abaffle hole is proportional to the hole number, i.e., the distance fromthe exhaust outlet. Also as shown in FIG. 10, the flow rate drasticallyvaries at the location around the 20th hole, which proves that the flowrate uniformity is very poor in the circumferential direction of thebaffle plate.

[0154] [Third Embodiment]

[0155] A third embodiment of the present invention is a porous baffleplate provided with the uniform-diameter baffle holes formed at uniformintervals. In this baffle plate, the hole intervals and the pore sizesare all uniform, but the length of the holes, i.e., the plate thicknessis varied in such a manner that can maintain a uniform average exhaustflow rate in the circumferential direction.

[0156]FIG. 11 shows the structure of a baffle plate 29 of the thirdembodiment of the present invention. FIG. 12 shows the structure of agas process chamber on which the baffle plate 29 of this embodiment ismounted. As shown in FIG. 12, the baffle plate 29 has a greaterthickness in the vicinity of the connecting port of the exhaust pipe 11so as to restrict an increase in exhaust flow rate per hole due to anexcessive differential suction pressure, thereby reducing a conductanceby the gas flow. At the upstream side of the gas flow, where thedifferential suction pressure decreases, the baffle plate 29 has asmaller thickness so as to increase the conductance, thereby obtaining auniform exhaust flow rate.

[0157] The length of each baffle hole 31 and the thickness of the baffleplate 29 required for obtaining the uniform exhaust flow rate aredetermined in the following manner.

[0158] The optimum thickness variation of the baffle plate 29 can beobtained by the relational expression in accordance with the secondembodiment of the present invention, with the length L₀ of the ithbaffle hole 31 being L_(i) and the pore size D_(i) being D₀.

P _(i)=[⁰ P ² −δL _(i) F _(i)/{(π/4)D ₀ ⁴}]^(0.5)  (44)

P _(i) =[P _(i−1) ² +δL _(m)(F ₀/2−F ₁/2−F ₂ −. . .−F _(i−1)) /{(π/4)D_(H) ⁴}]^(0.5)  (45)

F _(i)=(⁰ P ² P _(i) ²){(π/4)D ₀ ⁴ }/δL _(i) =F ₀ /m  (46 )

D ₀ =[δL _(i) F ₀/{(πm/4)(⁰ P ² −P _(i) ²)}]^(1/4)  (47)

[0159] Here, the above equation (44) is substituted in the equation (45)to obtain the following equation. $\begin{matrix}{\lbrack {}^{0} {P^{2} - {\delta \quad L_{i}{F_{i}/\{ {( {\pi/4} )D_{0}^{4}} \}}}} \rbrack ^{0.5} = \lbrack {}^{0} {P^{2} - {\delta \quad L_{i - 1}{F_{i - 1}/\{ {( {\pi/4} )D_{0}^{4}} \}}} + {\delta \quad {{L_{m}( {{F_{0}/2} - {F_{1}/2} - F_{2} - \cdots - F_{i - 1}} )}/\{ {( {\pi/4} )D_{H}^{4}} \}}}} \rbrack ^{0.5}} & (48)\end{matrix}$

[0160] Since the flow rates of the baffle holes 31 are equal to eachother, i.e., F_(i−1)/F_(i)=1, and a hole interval L_(m) is 2πr/m, thelength L_(i) of the ith baffle hole 31 can be determined as follows.$\begin{matrix}\begin{matrix}{L_{i} = \quad {L_{i - 1} - {{L_{m}( {D_{0}/D_{H}} )}^{4}( {{{F_{0}/2}F_{i}} + {{F_{1}/2}F_{i}} - {F_{1}/F_{i}} -} }}} \\ \quad {{F_{2}/F_{i}} - \cdots - {F_{i - 1}/F_{i}}} ) \\{= \quad {L_{i - 1} - {( {2\pi \quad {r/m}} )( {D_{0}/D_{H}} )^{4}\{ {{m/2} + {1/2} - ( {1 + 1 + \cdots + 1} )} \}}}} \\{= \quad {L_{i - 1} - {( {\pi \quad {r/m}} )( {D_{0}/D_{H}} )^{4}( {m + 3 - {2i}} )}}} \\{= \quad {L_{1} - {( {\pi \quad {r/m}} )( {D_{0}/D_{H}} )^{4}\{ {( {m - 1} ) + ( {m - 3} ) +} }}} \\{\quad  {( {m - 5} ) + \cdots + ( {m + 3 - {2i}} )} \}} \\{= \quad {L_{1} - {( {\pi \quad {r/m}} )( {D_{0}/D_{H}} )^{4}( {i - 1} ){( {m - i + 1} ).}}}}\end{matrix} & (49)\end{matrix}$

[0161] If the angle position of the first hole on the pitch circle inthe vicinity of the connecting port of the exhaust pipe 11 is 0°, andthe angle position of the n the hole that is the farthest away from theconnecting port is 180°, the relationship between n and the total holenumber m can be expressed as n=(m+2)/2, and the plate thickness L_(n) ofthe thinnest nth hole can be expressed as follows.

L _(n) =L ₁ −πr(D ₀ /D _(H))⁴(m ²−4)/4m  (50)

[0162] Since the allowable range of L₁ and L_(n) should be the minimumsuction pressure P* or larger, the following equations hold.

P ₁=[⁰ P ² −δL ₁ F ₁/{(π/4)D ₀ ⁴}]^(0.5) >P*  (51)

L ₁<(⁰ P ² −P* ²)(πm/4)D ₀ ⁴ /δF ₀  (52)

P ₁=[⁰ P ² −δF ₁ {L _(n) +πr(D ₀ /D _(H))⁴(m ²−4)/4m}/{(π/4)D ₀⁴}]^(0.5) >P*  (53)

L _(n)<(πm//4)(D ₀ D _(H))⁴ {(⁰ P ² −P* ²)D _(H) ⁴ /δF ₀ −r(1−4/m²)}  (54)

[0163] The allowable range of pore sizes can be obtained by thefollowing equation, which is obtained by substituting an arbitrarilyselected L_(n) in the above equation (54).

D ₀ >[L _(n)/[(πm/4){(⁰ P ² −P* ²)/δF ₀ −r(1−4/m ²)/D _(H)⁴}]]^(1/4)  (55)

[0164] As described so far, the optimum thickness variation of thebaffle plate for realizing uniform exhaust is determined by the equation(49). However, it is necessary to employ the restrictive conditions ofthe equations (52), (54), and (55) based on the limit of the lowestsuction pressure P* and the chamber pressure ⁰P.

[0165] Now, influences of the pore sizes of the baffle holes on theoptimum plate thickness variation are shown in Table 7 and Table 8.TABLE 7 COLUMN NUMBER 3-1 3-2 3-3 3-4 3-5 CHAMBER PRESSURE Pa 93.3 93.393.3 93.3 93.3 TOTAL GAS FLOW RATE sccm 1203 1203 1203 1203 1203TEMPERATURE ° C. 520 520 520 520 520 GAS VISCOSITY Pa · s 3.63E − 053.63E − 05 3.63E − 05 3.63E − 05 3.63E − 05 PORE SIZE mm 2.55 3.00 4.005.00 6.00 DUCT EQUIVALENT DIAMETER mm 27.3 27.3 27.3 27.3 27.3 NUMBER ofHOLES (ON THE 72 72 72 72 72 ENTIRE CIRCUMFERENCE) HOLE NUMBER I No. 137 1 37 1 37 1 37 1 37 PLATE THICKNESS Li mm 1.52 1 1.99 1 4.14 1 8.67 116.9 1 DIFFERENTIAL SUCITON Pa 89.9 38.7 40.9 17.7 24.1 5.2 20.2 2.118.8 1.0 PRESSURE Δ ° Pi DUCT INNER PRESSURE Pi sccm 3.4 54.6 52.4 75.669.2 88.1 73.2 91.2 74.5 92.3 FLOW RATE PER HOLE Fi sccm 16.71 16.7116.71 16.71 16.71 16.71 16.71 16.71 16.71 16.71 UNIFORMITY (m.m. METHOD)% 0.00% 0.00% 0.00% 0.00% 0.00%

[0166] TABLE 8 COLUMN COLUMN NUMBER 3-1 3-2 3-3 3-4 3-5 NUMBER 3-1 3-23-3 3-4 3-5 HOLE PORE SIZE (mm) HOLE PORE SIZE (mm) NUMBER 2.55 3 4 5 6NUMBER 2.55 3 4 5 6 1 1.52 1.99 4.14 8.67 16.9 19 1.13 1.25 1.79 2.925.0 2 1.49 1.94 3.97 8.25 16.0 20 1.12 1.22 1.70 2.71 4.5 3 1.46 1.893.80 7.84 15.2 21 1.10 1.20 1.62 2.51 4.1 4 1.44 1.84 3.64 7.44 14.4 221.09 1.17 1.55 2.33 3.8 5 1.41 1.79 3.48 7.06 13.6 23 1.08 1.15 1.472.16 3.4 6 1.38 1.74 3.33 6.68 12.8 24 1.07 1.13 1.41 2.00 3.1 7 1.361.69 3.18 6.32 12.0 25 1.06 1.11 1.35 1.85 2.8 8 1.34 1.65 3.04 5.9711.3 26 1.05 1.09 1.29 1.72 2.5 9 1.31 1.60 2.90 5.64 10.6 27 1.04 1.081.24 1.59 2.2 10 1.29 1.56 2.77 5.31 9.9 28 1.03 1.06 1.20 1.48 2.00 111.27 1.52 2.64 5.00 9.3 29 1.03 1.05 1.16 1.38 1.8 12 1.25 1.48 2.514.70 8.7 30 1.02 1.04 1.12 1.29 1.6 13 1.23 1.44 2.40 4.41 8.1 31 1.011.03 1.09 1.21 1.4 14 1.21 1.41 2.28 4.13 7.5 32 1.01 1.02 1.06 1.15 1.315 1.19 1.37 2.17 3.86 6.9 33 1.01 1.01 1.04 1.09 1.2 16 1.18 1.34 2.073.61 6.4 34 1.00 1.01 1.02 1.05 1.1 17 1.16 1.31 1.97 3.37 5.9 35 1.001.00 1.01 1.02 1.00 18 1.14 1.28 1.87 3.14 5.4 36 1.00 1.00 1.00 1.011.00 37 1.00 1.00 1.00 1.00 1.00

[0167] The baffle plates 29 of the column numbers 3-1 to 3-5 each haveseventy-two baffle holes having uniform pore sizes and arranged atuniform intervals, and has a pitch circle radius r of 120 mm. With thepore sizes being varied, a simulation was performed on the optimumthickness variation required for uniform exhaust. The process conditionsand the duct radiuses are the same as in the case shown in FIG. 5.

[0168] For ease of processing a baffle plate 29, the minimum thicknessL_(n) of the baffle plate 29 was set at 1 mm, and the minimum limit poresize D₀>2.55 mm for the baffle holes 31 was obtained by the equation(55). Experiments were then carried out on the cases where the minimumlimit pore size D₀ of 3 mm to 6 mm. Table 7 shows the plate thicknessescorresponding to the baffle holes 31 at the downstream side and theupstream side of the gas flow, the duct inner pressures, thedifferential pressures between both sides of the baffle holes 31, andthe gas flow rates per hole in the cases shown by the column numbers 3-1to 3-5.

[0169] In Table 8, the plate thicknesses of the respective baffle holesin greater details in the cases indicated by the column numbers 3-1 to3-5. In accordance with Table 8, the flow rates of the respective casesare uniform, regardless of the locations of the baffle hole 31. As aresult, the variation rate at the location where the pore size is 5 mmgreater is too high, and accordingly, it can be said that it is suitableto design the thickness of a baffle plate with the baffle hole diameters3 to 4 mm.

[0170] As is apparent from the equation (50), by the above method forobtaining uniform exhaust by adjusting the thickness of the baffle plate29, the optimum thicknesses can be obtained regardless of the processconditions, such as the gas temperature, pressure, flow rate, andviscosity. Therefore, the results of a simulation performed underdifferent process conditions are omitted. Other test results in caseswhere the number of baffle holes is different and the equivalentdiameter of the duct is different can be easily obtained by theforegoing relational expressions in the same manner. However, it shouldbe understood that the range in which the baffle plate 29 of the thirdembodiment of the present invention can be obtained is limited by theconditions specified by the equation (55).

[0171] [Fourth Embodiment]

[0172] A fourth embodiment of the present invention is a slit-typebaffle plate provided with slits (baffle slits) having various widths soas to obtain uniform exhaust.

[0173]FIG. 13 shows the structure of a baffle plate 33 of the fourthembodiment. FIG. 14 shows the structure of a gas process chamber onwhich the baffle plate is mounted. The baffle plate is a porous type, inwhich the conductance is adjusted by varying the intervals and diametersof the baffle holes formed around the wafer, or varying the thickness ofthe baffle plate, so as to obtain uniform exhaust. In the baffle plateof this embodiment, on the other hand, the conductance of the gas flowthrough exhaust slits (baffle slits) 35 that penetrate the surroundingarea of the wafer 1 is adjusted. The widths of the slits 35 and thethickness of the baffle plate 33 are varied in the circumferentialdirection, thereby obtaining uniform exhaust in the circumferentialdirection.

[0174] This baffle plate 33 is advantageous in that it is capable ofcontinuously exhausting in the circumferential direction. Accordingly,the baffle plate 33 is suitable as a low differential pressure baffle(great conductance baffle) for realizing uniform exhaust in alow-pressure process chamber.

[0175] Next, theoretical equations for designing the baffle plate 33provided with the slits will be described. Here, the equations forobtaining a fluid pressure loss of the baffle plate provided with theslits are analyzed, and the relational expressions for determining theoptimum slit widths and the thickness variation of baffle plate 33.

[0176] After the equivalent diameter D_(H) of the cross section of arectangular pipe with a long side a and a short side b, the pipediameter of the Fanning's equation is tuned into the followingequations, with a being infinite.

D _(H)=4×cross section of the pipe/circumference =4ab/(2a+2b)→2b  (56)

Re=D _(Hρ) U/μ  (57)

[0177] (U is the average flow rate in cross section)

[0178] In the equation (57), Re indicates the Reynold's number, Uindicates the average flow rate in cross section, and ρ indicates thedensity of the fluid. The fluid pressure loss Δp is expressed asfollows.

ΔP=32 μLU/(b ² X/2)  (58)

[0179] A value 16/3 is then substituted as X in the equation (58), andthe fluid pressure loss Δp is expressed as follows.

ΔP=12 μLU/b ²

f=24/Re  (59)

[0180] Meanwhile, the friction loss coefficient f is indicated by 24/Re.Taking into account an influence of an air expansion on the flow ratedue to a variation in pressure, the following equation is obtained inthe same manner as in the foregoing embodiment.

Δ⁰ P _(i)=⁰ P−(⁰ P ²−24 μL _(i) RT ⁰ G _(i) /Mb _(i) ²) ^(0.5)  (60)

[0181] wherein: i indicates a circumferential angle, with the locationof the connecting port of the exhaust pipe being the origin; Δ⁰P₁indicates a differential pressure between the inner pressure P_(i) ofthe exhaust duct at a location i and the chamber inner pressure ⁰P;L_(i) indicates the thickness of the slit plate at the location i; b_(i)indicates the slit width at the location of the circumferential angle i;and °G_(i) indicates the mass velocity of the gas flowing from thechamber into the area having the unit angle width of the correspondingslit i. To determine the slit width required for obtaining uniformexhaust in the circumferential direction, and the thickness variation ofthe baffle plate 33 in the circumferential direction, the followingcalculation is made.

[0182] The relationship between the pressure loss and the gas flow ratebetween the angle positions i+di and i in the exhaust duct 5 isapproximately expressed as follows. $\begin{matrix}\begin{matrix}{{\Delta \quad P_{{i + {di}},i}} = \quad {P_{i + {di}} - P_{i}}} \\{= \quad {\{ {P_{i}^{2} + {64µ\quad {r({di})}( {\pi/180} ){{RTG}_{{i + {di}},i}/{MD}_{H}^{2}}}} \}^{0.5} - P_{i}}}\end{matrix} & (61)\end{matrix}$

[0183] wherein the r(di)(π/180) is the length of the exhaust duct 5 perangle (di), with the radius of the pitch circle of the duct being r, andG_(i+di,i) is the mass flow rate of the gas flowing through the exhaustduct between the angle positions (i+di)° and the i°. D_(H) is anequivalent diameter of the exhaust duct 5.

[0184] From the relationship between Δ⁰P_(i) and ΔP_(i+di), thefollowing equation holds.

Δ⁰ P _(i+di,i)=Δ⁰ P _(i) −ΔP _(i+di,i)  (62)

[0185] From this equation, the following equation holds. $\begin{matrix}\begin{matrix}{{\Delta^{0}P_{i + {di}}} = \quad {{0P} - P_{i + {di}}}} \\{= \quad {P_{i} - \{ {P_{i}^{2} + {64{µ( {\pi \quad {r/180}} )}({di}){{RTG}_{{i + {di}},i}/{MD}_{H}^{2}}}} \}^{0.5} + {\Delta^{0}P_{i}}}} \\{= \quad {P_{i} - \{ {P_{i}^{2} + {64{µ( {\pi \quad {r/180}} )}({di}){{RTG}_{{i + {di}},i}/{MD}_{H}^{2}}}} \}^{0.5} +^{0}P -}} \\{\quad ( {}^{0}{P^{2} - {24µ\quad L_{i}{RT}^{0}{G_{i}/{Mb}_{i}^{2}}}} )^{0.5}}\end{matrix} & (63)\end{matrix}$

[0186] wherein ⁰G_(i) is the mass flow rate of the gas passing throughthe slits per 1° open area at the angle i° position. With the total flowrate at the time of uniform exhaust being ⁰F, and the average exhaustflow rate f being ⁰F/360 [sccm/deg], the following equation holds.

⁰ G _(i) =f(1E-6/60)(M/0.0224)/{(b _(i))(πr/180)}  (64)

[0187] The F_(i+di,i) is the flow rate [sccm] of the gas flowing throughthe exhaust duct 5 between i° and i+di°, which is an approximate valueof the total flow rate of the gas discharged from the slits 35 into theexhaust duct 5 between 180 and i°.

F _(i+di,i)=(180−i)f=(180−i)⁰ F/360

G _(i+di,i) =F _(i+di,i)(1E-6/60)(M/0.0224)/{(π/4)D _(H) ²}

G _(i+di,i)=(180−i)f(1E-6/60)(M/0.0224) /(π/4)D _(H) ²}  (65)

[0188] The equations (61) and (63) are then substituted in the equations(64) and (65) to obtain the following equations.

ΔP _(i+di,i) =[P _(i) ²+(4)(64)μRT rf(di)(1/180)(180−i)(1E-6/60)(1/0.0224)/D _(H) ⁴]^(0.5) −P _(i)  (66)

Δ ⁰ P _(i+di) =P _(i) −{P _(i) ²+(4)(64)μRTrf(di)(1/180)(180−i)(1E-6/60)(1/0.0224)/D _(H) ⁴}^(0.5)+⁰ P−{⁰ P ²−24μL _(i) RTf(180/πr)(1E-6/60) (1/0.0224)/b _(i) ³}^(0.5)  (67)

[0189] To simplify the above equations, the constants can be expressedas follows.

α=24μRT(180/π)(1E-6/60)(1/0.0224)  (68)

β=(4)(64)μRT(1E-6/60)(1/0.0224)/D _(H) ⁴  (69)

ΔP _(i+di,i) =[P _(i) ² +βfr(di)(1/180)(180−i)]^(0.5) −P _(i)  (70)

Δ⁰ P _(i+di) =P _(i) −{P _(i) ² +βfr(di)(1/180) (180−i)}^(0.5)+⁰ P−{⁰ P² −αfL _(i) /rb _(i) ³}^(0.5)  (71)

[0190] Since the pressure P₀ immediately below the slit at the firstangle 0° is equal to or higher than the suction limit pressure P*, thefollowing equation holds.

P ₀=(⁰ P ² −αfL ₀ /rb ₀ ³)^(0.5) >P*  (72)

[0191] The conditions of the smallest width b₀ of the slits can beexpressed as follows.

b ₀>{(αfL ₀ /r)/(⁰ P ² −P* ²)}^(1/3)  (73)

[0192] With the pressure immediately below the angle di° being P_(di),the average exhaust flow rate F₀ in the first section is expressed as(180-di)f. Accordingly, the following equation holds. $\begin{matrix}{{\Delta^{0}P_{0 + {di}}} = \quad {{0P} - P_{0 + {di}}}} \\{= \quad {P_{0} - \{ {P_{0}^{2} + {\beta \quad {{fr}({di})}( {1/180} )( {180 - 0} )}} \}^{0.5} +^{0}P -}} \\{\quad \{ {}^{0}{P^{2} - {\alpha \quad {{fL}_{0}/{rb}_{0}^{3}}}} \}^{0.5}}\end{matrix}$

 ⁰ P−P _(0+di) =P ₀ −{P ₀ ² +βfr(di)(1/180)(180−0) }^(0.5)+⁰ P−{⁰ P ²−αfL ₀ /rb ₀ ³}^(0.5)

P _(di) =−P ₀ +{P ₀ ² +βfr(di)(1/180)(180−0)}^(0.5)+{⁰ P ² −αfL ₀ /rb ₀³}^(0.5)

[0193] Strictly speaking, the differential equations can be calculatedby a Runge-Kutta method using a computer. However, the principles willbe described below by the Euler's method, which is simplified for easeof explanation.

[0194] Based on the smallest slit width b₀ at the angle position 0°where the plate thickness L₀ is constant, or based on the greatest platethickness L₀ where the slit width b₀ is constant, P₀ is obtained fromthe equation (72), and P_(i) is obtained from the following equation.

P ₁ =−P ₀ +{P ₀ ² +βfr(1)(1/180)(180−0)}^(0.5)+{⁰ P ² −αfL ₀ /rb ₀³}^(0.5)  (74)

[0195] With the obtained P_(i), the slit width b_(i+1) or the platethickness L_(i+1) can be obtained from the following equations (75) and(76).

b _(i=1) [αfL _(i+1) /r{ ⁰ P ² −P _(i) ² −βfr(1)(1/180)(180−i)}]^(1/3)  (75)

L _(i+1) =b _(i+1)3(r/αf){⁰ P ² −P _(i) ² −βfr(1)(1/180) (180−i)}  (76)

[0196] The above equations (75) and (76) are substituted in thefollowing equation, so as to obtain the value P_(i+1).

P _(i+1)={⁰ P ² −αfL _(i+1) /rb _(i+1) ³}^(0.5) ={P _(i) ²+βfr(1)(1/180)(180−i)}^(0.5)  (77)

[0197] The inner pressures of the exhaust duct 5 in a case where i is 0,1, 2, . . . are sequentially calculated, so that the slit width b₁ foruniform exhaust and the variation of the thickness L_(i) of the baffleplate 33 are determined.

[0198] Table 9 shows specific examples of the uniform-thicknessslit-type baffle plate 33 obtained by determining the variation of theslit widths required for obtaining uniform exhaust in the chamber. Theprocess conditions of the data shown in Table 9 are the same as theprocess conditions as in Table 1. TABLE 9 COLUMN NUMBER 4-1 4-2 4-3CHAMBER PRESSURE Pa 93.3 93.3 93.3 TOTAL GAS FLOW RATE sccm 1203 12031203 TEMPERATURE ° C. 520 520 520 GAS VISCOSITY Pa · s 3.63E − 05 3.63E− 05 3.63E − 05 BAFFLE PLATE THICKNESS mm 1 1 2 DUCT EQUIVALENT DIAMETERmm 27.3 27.3 27.3 MAXIMUM & MINIMUM WIDTHS MAXIMUM MINIMUM MAXIMUMMINIMUM MAXIMUM MINIMUM SLIT WIDTH mm 1.21 1.0 1.92 1.2 2.34 1.5DIFFERENTIAL SUCITON Pa 23.5 49.6 5.3 24.1 5.9 24.8 PRESSURE DUCT INNERPRESSURE Pa 69.8 43.8 88.0 69.2 87.5 68.5 FLOW RATE PER UNIT ANGLE sccm3.34 3.34 3.34 3.34 3.34 3.34 UNIFORMITY (m.m. METHOD) % 0.00% 0.00%0.00% COLUMN NUMBER 4-4 4-5 CHAMBER PRESSURE Pa 93.3 93.3 TOTAL GAS FLOWRATE sccm 1203 1203 TEMPERATURE ° C. 520 520 GAS VISCOSITY Pa · s 3.63E− 05 3.63E − 05 BAFFLE PLATE THICKNESS mm 3 3 DUCT EQUIVALENT DIAMETERmm 27.3 27.3 MAXIMUM & MINIMUM WIDTHS MAXIMUM MINIMUM MAXIMUM MINIMUMSLIT WIDTH mm 1.88 1.5 3.39 1.8 DIFFERENTIAL SUCITON Pa 18.3 41.6 2.921.0 PRESSURE DUCT INNER PRESSURE Pa 75.0 51.7 90.5 72.3 FLOW RATE PERUNIT ANGLE sccm 3.34 3.34 3.34 3.34 UNIFORMITY (m.m. METHOD) % 0.00%0.00%

[0199] The lowest limit of the slit widths in a case where the thicknessL₀ of the baffle plate 33 is 0.92 mm. Accordingly, the thicknesses are 1mm, 2 mm, and 3mm, while the smallest slits widths b₀ are 1 mm, 1.2 mm,1.5 mm, and 1.8 mm, as shown in Table 9. A simulation was performed foreach of the cases. Under each of the numbers shown in Table 9, the innerpressures of the exhaust duct 5 corresponding to the smallest slit widthand the greatest slit width, the differential pressure (differentialsuction pressure) between both sides of each of the slits 35, the flowrate of the gas discharged from the slits per unit angle 1°, and theuniformity of the exhaust flow rates are shown.

[0200] As can be seen from Table 9, the exhaust flow rate is uniform inany case. Where the plate thickness is as small as 1 mm, the variationrange of the slit widths is narrow, and the variation of the widths inthe circumferential direction is in a very narrow range of 1 mm to 1.21mm. This implies that the required precision in processing andassembling of the baffle plate 33 is very high. However, in the case ofthe column number 4-5 shown in Table 9 in which a baffle plate having athickness of 3 mm, the slit widths vary in the range of 1.8 mm to 3.39mm, and the variation range on the circumference is greater.

[0201] As is apparent from Table 9, with the baffle plate 33 of thisembodiment, the optimum variation of the plate thickness can be easilyobtained.

[0202] It should be understood that the baffle plate is not necessarilyformed by an integral component, but may be made up of a plurality ofcomponents.

[0203] [Fifth Embodiment]

[0204] A fifth embodiment of the present invention is a baffle platehaving slits of uniform widths. The thickness of this baffle plate isvaried so as to obtain uniform exhaust.

[0205]FIG. 15 shows the structure of the baffle plate of the fifthembodiment of the present invention. FIG. 16 shows the structure of agas process chamber on which the baffle plate of this embodiment ismounted. As shown in FIGS. 15 and 16, to obtain uniform exhaust in thechamber by a slit-type baffle plate 37, the equation (76) of the fourthembodiment is used so as to optimize the thickness variation of thebaffle plate 37, while maintaining the widths of through slits 39uniform.

[0206] In order to keep the exhaust flow rates in the circumferentialdirection constant, the thickness variation of the baffle plate 37 inthe circumferential direction was examined under the same processconditions as in the cases shown in Table 1. More specifically, thewidths of the slits 39 were made uniform in the circumferentialdirection, while the widths of the other slits 39 were varied in therange of 1.8 mm to 2.5 mm. The greatest thickness of the baffle plate 37was 5 mm or 10 mm, the uniformity of the exhaust flow rates wereexamined through simulations. Table 10 shows the result of thesimulations. TABLE 10 COLUMN NUMBER 5-1 5-2 5-3 CHAMBER PRESSURE Pa 93.393.3 93.3 TOTAL GAS FLOW RATE sccm 1203 1203 1203 TEMPERATURE ° C. 520520 520 GAS VISCOSITY Pa · s 3.63E − 05 3.63E − 05 3.63E − 05 SLIT WIDTHmm 1.8 2.1 2.1 DUCT EQUIVALENT DIAMETER mm 27.3 27.3 27.3 MAXIMUM &MINIMUM WIDTHS MAXIMUM MINIMUM MAXIMUM MINIMUM MAXIMUM MINIMUM SLITTHICKNESS mm 2.47 5.0 0.98 5.0 5.98 10 DIFFERENTIAL SUCITON Pa 17.0 39.74.0 22.4 27.7 56.5 PRESSURE DUCT INNER PRESSURE Pa 76.3 53.6 89.4 70.965.6 36.8 FLOW RATE PER UNIT ANGLE sccm 3.34 3.34 3.34 3.34 3.34 3.34UNIFORMITY % 0.00% 0.00% 0.00% COLUMN NUMBER 5-4 5-5 CHAMBER PRESSURE Pa93.3 93.3 TOTAL GAS FLOW RATE sccm 1203 1203 TEMPERATURE ° C. 520 520GAS VISCOSITY Pa · s 3.63E − 05 3.63E − 05 SLIT WIDTH mm 2.5 2.0 DUCTEQUIVALENT DIAMETER mm 27.3 27.3 MAXIMUM & MINIMUM WIDTHS MAXIMUMMINIMUM MAXIMUM MINIMUM SLIT WIDTH mm 3.22 10 6.53 10 DIFFERENTIALSUCITON Pa 7.9 27.4 37.2 79.3 PRESSURE DUCT INNER PRESSURE Pa 85.5 66.056.1 14.1 FLOW RATE PER UNIT ANGLE sccm 3.34 3.34 3.34 3.34 UNIFORMITY %0.00% 0.00%

[0207] When the widths of the slits are 3 mm or greater, the greatestthickness of the baffle plate 37 on the side of the exhaust pipe 11 isas thick as several centimeters, which is not a practical value. This isbecause the fluid pressure loss of the slits 39 is inverselyproportional to the cube of the width of each slit 39, while beingproportional to the thickness of the baffle plate 37. Also, if the innerpressure of the exhaust duct 5 is low and the differential suctionpressure is high enough, the widths of the slits 39 are preferablymaintained at a small constant value, so that the exhaust flow rate inthe circumferential direction can be adjusted while maintaining athickness variation within a range of 1 mm to 3 mm.

[0208] As described above, in accordance with the fifth embodiment ofthe present invention, the uniform-width slit-type baffle plate 37having the optimum shape can be efficiently and readily designed.

[0209] [Sixth Embodiment]

[0210]FIG. 17 shows the structure of a baffle plate of a sixthembodiment of the present invention, and FIG. 18 shows the structure ofa gas process chamber on which the baffle plate of this embodiment ismounted. As shown in FIG. 18, a baffle plate 41 of this embodiment is atype of porous baffle plate that varies in thickness. The shape of eachbaffle hole 43 is not circular but rectangular. As in this embodiment,the shape of baffle holes (or baffle passages) of the present inventionis not limited to a rectangle. Also, in a case of circular baffle holes,they are not necessarily arranged on a single pitch circle, but may bearranged on a plurality of pitch circles having different circles.

[0211] In this embodiment, however, the conductance of the baffle holes(or baffle passages) should be made equal to the conductance of circularbaffle holes arranged on a single pitch circle. In the case of therectangular baffle holes 43, the equivalent diameter Dh=2ab/(a+b), whichis obtained from the long side a and the short side b, should be madeequal to the diameter of a desired circular hole.

[0212] Meanwhile, a technique of dividing one baffle hole into aplurality of baffle holes having the same functions is alsoadvantageous, and this technique may be applied to either an entirepitch circle or a partial pitch circle. For instance, in a case where awafer is processed by a method using plasma, it is necessary to preventa plasma gas from passing through the baffle plate and flowing towardthe exhaust side. Therefore, with the baffle plate of the secondembodiment in which the diameters of the baffle holes are varied in thecircumferential direction, each baffle hole having a great diameter mayhave to be replaced by a plurality of baffle holes having smalldiameters. In such a case, the fluid pressure loss based on the gas flowrate divided by the number of the baffle holes is partially applied tothe relational expressions of the foregoing embodiments, so as todetermining the diameters of the baffle holes.

[0213] [Seventh Embodiment]

[0214] In the foregoing embodiments, only one of the factors includingthe hole intervals, the pore sizes, the plate thickness, or the shape ofthe slits, is varied to obtain uniform exhaust. In a seventh embodimentof the present invention, on the other hand, a plurality of factors arevaried at the same time. For instance, the first embodiment and thesecond embodiment of the present invention may be combined. In such acase, baffle holes having smaller pore sizes are formed between theregular baffle holes, so that the intervals between the baffle holesnear the connecting port of the exhaust pipe can be prevented frombecoming too long.

[0215] However, it should be understood that varying a plurality offactors at the same time is costly, and therefore, this embodimentshould be employed only for special use.

[0216] [Eighth Embodiment]

[0217]FIG. 19 shows the structure of a gas process chamber of an eighthembodiment of the present invention, and FIG. 20 is a plan view of thisgas process chamber.

[0218] As shown in FIGS. 19 and 20, the gas process chamber of thisembodiment comprises a chamber 45 provided with a chamber wall 46 thatsurrounds the wafer stand 3. In this gas process chamber, exhaust slits47 are formed at the bottom end of the chamber wall 46. The heights ofthe exhaust slits 47 are varied to obtain uniform exhaust as in theforegoing embodiments.

[0219] Varying the heights of the exhaust slits 47 around the waferstand 3 has hydrodynamically the same effects as the fourth embodimentin which the widths of the slits 35 on the slit-type baffle plate 33 arevaried around the wafer stand 3. In view of this, it can be said thatthe gas process chamber of this embodiment is a modification of the gasprocess chamber of the fourth embodiment.

[0220] [Ninth Embodiment]

[0221]FIG. 21 is a block diagram showing the structure of an apparatusfor producing a baffle plate of the present invention. In this blockdiagram, the solid lines indicate the data flow, and the broken linesindicate the flow of control signals. As shown in FIG. 21, thisapparatus for producing a baffle plate comprises an input/output unit50, a storage unit 51, an arithmetic operation unit 53, a control unit55, and a work unit 57. Parameters such as the characteristics of theprocess gas, the process conditions, the shape of the exhaust duct, thesize of the process chamber, are inputted in the input/output unit 50.The arithmetic operation unit 53 is connected to the storage unit 51.The work unit 57 is connected to the input/output unit 50. The controlunit 55 is connected to the input/output unit 50, the storage unit 51,the arithmetic operation unit 53, and the work unit 57.

[0222] Depending on the type of process to be performed, the work unit57 is formed by a lathe, a drilling machine, a boring machine, or amilling machine. When baffle holes are formed in the baffle plate, forinstance, a drilling machine is used.

[0223] Referring now to a flowchart shown in FIG. 22, the operation ofthe apparatus for producing a baffle plate having the above structurewill be described.

[0224] In step S1, the parameters such as the characteristics and theprocess conditions of the process gas, the shape of the exhaust duct,and the size of the process chamber are inputted into the input/outputunit 50. The inputted parameters are stored in the storage unit 51.

[0225] In step S2, the control unit 55 controls the arithmetic operationunit 53 based on a flow rate calculating program according to theHagen-Poiseuille's law, which program is stored in the storage unit 51in advance. More specifically, in accordance with the above program,baffle holes are virtually formed on the baffle plate. The arithmeticoperation unit 53 calculates the pressure difference between the twosides of the baffle plate and a pressure variation in the exhaust ductin accordance with the Hagen-Poiseuille's law, thereby determining theflow rate of the gas flowing through the baffle holes. The results ofthe calculation are temporarily stored in the storage unit 51 andtransmitted to the control unit 55.

[0226] In step S3, the control unit 55 determines the locations and poresizes of the baffle holes in such a manner that makes the flow rates ofthe baffle holes uniform. In step S4, the control unit 55 supplies thedata indicating the optimum locations of the baffle holes to the workunit 57.

[0227] In step S5, based on the supplied data, the work unit 57processes the baffle plate. The operation information of the work unit57 is supplied to the control unit 55, which in turn controls the workunit 57 in accordance with the supplied operation information.

[0228] With the above apparatus for producing a baffle plate of theninth embodiment of the present invention, any of the baffle plates ofthe foregoing embodiments can be readily produced.

1. A baffle plate that parts a process space in which a chemical processis carried out with a supplied gas from a duct that is adjacent to theprocess space for discharging an exhaust gas generated as a result ofthe chemical process, said baffle plate characterized in that, after aplurality of through holes are virtually formed at desired locations onthe baffle plate, the plurality of through holes are actually formed atthe desired location so that flow rates of the exhaust gas at theplurality of through holes become uniform.
 2. A baffle plate that partsa process space in which a chemical process is carried out with asupplied gas from a duct that is adjacent to the process space fordischarging an exhaust gas generated as a result of the chemicalprocess, said baffle plate characterized in that, through holes areformed at a plurality of locations on the baffle plate, depending onpressure differences between two sides of the baffle plate.
 3. Thebaffle plate as claimed in claim 2, wherein the through holes are formedin accordance with a pressure variation of the exhaust gas along aflowing path of the exhaust gas inside the duct.
 4. The baffle plate asclaimed in claim 3, wherein the through holes are formed so that a flowrate of the exhaust gas flowing through the through holes calculated bythe Hagen-Poisueille's equation becomes constant.
 5. The baffle plate asclaimed in claim 2, wherein at least three through holes are arranged atvarious intervals along a flowing path of the exhaust gas inside theduct.
 6. The baffle plate as claimed in claim 2, wherein at least twothrough holes having different pore sizes are formed.
 7. A baffle platethat parts a process space in which a chemical process is carried outwith a supplied gas from a duct that is adjacent to the process spacefor discharging an exhaust gas generated as a result of the chemicalprocess, and a plurality of through holes are formed at desiredlocations, said baffle plate characterized in that, the baffle platevaries in thickness at two or more locations among the desiredlocations.
 8. A baffle plate that parts a process space in which achemical process is carried out with a supplied gas from a duct forexhausting an exhaust gas generated as a result of the chemical process,said baffle plate characterized in that, slits that penetrate throughthe baffle plate and vary in width along with a flowing path of theexhaust gas in the duct are formed in accordance with pressuredifferences between both sides of the baffle plate, the pressuredifferences varying depending on locations on the baffle plate.
 9. Abaffle plate that parts a process space in which a chemical process iscarried out with a supplied gas from a duct that is adjacent to theprocess space so as to discharge an exhaust gas generated as a result ofthe chemical process, said baffle plate characterized in that slits thatpenetrate through the baffle plate and have uniform widths are formedalong a flowing path of the exhaust gas inside the duct, and the baffleplate varies in thickness along the flowing path.
 10. A gas processapparatus that comprises: a process space including a stand on which anobject to be processed is placed, and a gas supply unit for supplying agas to the object to be processed so as to perform a chemical process onthe object placed on the stand; a duct that is adjacent to the processspace so as to discharge an exhaust gas generated as a result of thechemical process; and a discharging unit that is connected to the ductfor discharging the exhaust gas, said gas process apparatuscharacterized by further comprising a partition unit that parts the ductfrom the process space, and adjusts a flow rate of the exhaust gasflowing from the process space to the duct depending on pressuredifferences between both sides of a boundary surface, the pressuredifferences varying with locations on the boundary surface between theprocess space and the duct.
 11. A method of producing a baffle platethat parts a process space in which a chemical process is carried outwith a supplied gas from a duct that is adjacent to the process space soas to discharge an exhaust gas generated as a result of the chemicalprocess, said method comprising the steps of: calculating pressuredifferences between both sides of the baffle at desired locations on thebaffle plate; and forming through holes at a plurality of locations onthe baffle plate, depending on the calculated pressure differences. 12.A method of producing a baffle plate that parts a process space in whicha chemical process is carried out with a supplied gas from a duct thatis adjacent to the process space so as to discharge an exhaust gasgenerated as a result of the chemical process, said method comprisingthe steps of: calculating pressure differences between both sides of thebaffle plate, the pressure differences varying with locations on thebaffle plate, and a pressure variation of the exhaust gas along aflowing path of the exhaust gas inside the duct; and forming throughholes at a plurality of locations on the baffle plate in accordance withthe calculated pressure differences and the pressure variation.
 13. Amethod of producing a baffle plate that parts a process space in which achemical process is carried out with a supplied gas from a duct that isadjacent to the process space for discharging an exhaust gas generatedas a result of the chemical process, said method comprising the step offorming a plurality of through holes in the baffle plate so that a flowrate of the exhaust gas calculated in accordance with theHagen-Poiseuille's law becomes constant.
 14. An apparatus for producinga baffle plate that parts a process space in which a chemical process iscarried out with a supplied gas from a duct that is adjacent to theprocess space for discharging an exhaust gas generated as a result ofthe chemical process, said apparatus comprising: a calculating unit thatcalculates pressure differences between both sides of the baffle plateat various locations on the baffle plate; and a hole forming unit thatforms through holes at a plurality of locations on the baffle plate inaccordance with the pressure differences calculated by the calculatingunit.
 15. The apparatus as claimed in claim 14, wherein: the calculatingunit calculates a pressure variation of the exhaust gas along a flowingpath of the exhaust gas inside the duct; and the hole forming unit formsthe through holes at the plurality of locations on the baffle plate inaccordance with the pressure differences and the pressure variationcalculated by the calculating unit.
 16. An apparatus for producing abaffle plate that parts a process space in which a chemical process iscarried out with a supplied gas from a duct that is adjacent to theprocess space for discharging an exhaust gas generated as a result ofthe chemical process, said apparatus comprising: a calculating unit thatcalculates hole forming locations so that flow rates of the exhaust gasat through holes formed in the baffle plate calculated in accordancewith the Hagen-Poiseuille's law become uniform; and a hole forming unitthat forms the through holes at the hole forming locations calculated bythe calculating unit.